Bitmap/Read a PPM file

From Rosetta Code
Task
Bitmap/Read a PPM file
You are encouraged to solve this task according to the task description, using any language you may know.

Using the data storage type defined on this page for raster images, read an image from a PPM file (binary P6 prefered). (Read the definition of PPM file on Wikipedia.)

Task: Use write ppm file solution and grayscale image solution with this one in order to convert a color image to grayscale one.

11l

Translation of: Python
T Colour = BVec3

V black = Colour(0, 0, 0)
V white = Colour(255, 255, 255)

T Bitmap
   Int width, height
   Colour background
   [[Colour]] map

   F (width = 40, height = 40, background = white)
      assert(width > 0 & height > 0)
      .width = width
      .height = height
      .background = background
      .map = (0 .< height).map(h -> (0 .< @width).map(w -> @@background))

   F fillrect(x, y, width, height, colour = black)
      assert(x >= 0 & y >= 0 & width > 0 & height > 0)
      L(h) 0 .< height
         L(w) 0 .< width
            .map[y + h][x + w] = colour

   F set(x, y, colour = black)
      .map[y][x] = colour

   F get(x, y)
      R .map[y][x]

   F togreyscale()
      L(h) 0 .< .height
         L(w) 0 .< .width
            V (r, g, b) = .get(w, h)
            V l = Int(0.2126 * r + 0.7152 * g + 0.0722 * b)
            .set(w, h, Colour(l, l, l))

   F writeppmp3()
      V magic = "P3\n"
      V comment = "# generated from Bitmap.writeppmp3\n"
      V s = magic‘’comment‘’("#. #.\n#.\n".format(.width, .height, 255))
      L(h) (.height - 1 .< -1).step(-1)
         L(w) 0 .< .width
            V (r, g, b) = .get(w, h)
            s ‘’= ‘   #3 #3 #3’.format(r, g, b)
         s ‘’= "\n"
      R s

F tokenize(fstr)
   [String] tokens
   L(line) fstr.split("\n")
      I !line.starts_with(‘#’)
         L(t) line.split(‘ ’, group_delimiters' 1B)
            tokens.append(t)
   R tokens

F ppmp3tobitmap(fstr)
   V tokens = tokenize(fstr)
   V tokeni = -1
   F nexttoken()
      @tokeni++
      R @tokens[@tokeni]
   assert(‘P3’ == nexttoken(), ‘Wrong filetype’)
   V width  = Int(nexttoken())
   V height = Int(nexttoken())
   V maxval = Int(nexttoken())
   V bitmap = Bitmap(width, height, Colour(0, 0, 0))
   L(h) (height - 1 .< -1).step(-1)
      L(w) 0 .< width
         V r = Int(nexttoken())
         V g = Int(nexttoken())
         V b = Int(nexttoken())
         bitmap.set(w, h, Colour(r, g, b))

   R bitmap

V ppmtxt = |‘P3
             # feep.ppm
             4 4
             15
              0  0  0    0  0  0    0  0  0   15  0 15
              0  0  0    0 15  7    0  0  0    0  0  0
              0  0  0    0  0  0    0 15  7    0  0  0
             15  0 15    0  0  0    0  0  0    0  0  0
             ’

V bitmap = ppmp3tobitmap(ppmtxt)
print(‘Grey PPM:’)
bitmap.togreyscale()
print(bitmap.writeppmp3())
Output:
Grey PPM:
P3
# generated from Bitmap.writeppmp3
4 4
255
     0   0   0     0   0   0     0   0   0     4   4   4
     0   0   0    11  11  11     0   0   0     0   0   0
     0   0   0     0   0   0    11  11  11     0   0   0
     4   4   4     0   0   0     0   0   0     0   0   0

Action!

Part of the task responsible for conversion from RGB color image into a grayscale image can be found in the module RGB2GRAY.ACT. File D:PPM6.PPM can be generated by task Bitmap/Write a PPM file.

INCLUDE "H6:RGB2GRAY.ACT" ;from task Grayscale image

PROC DecodeSize(CHAR ARRAY s BYTE POINTER width,height)
  BYTE i

  width^=ValB(s)
  i=1
  WHILE i<=s(0) AND s(i)#32
  DO
    s(i)=32
    i==+1
  OD
  height^=ValB(s)
RETURN

PROC LoadHeader(RgbImage POINTER img
  CHAR ARRAY format BYTE dev)
  CHAR ARRAY line(255)
  BYTE header,size,max,width,height

  header=0 size=0 max=0
  WHILE max=0
  DO
    InputSD(dev,line)
    IF line(0)>0 AND line(1)#'# THEN
      IF header=0 THEN
        IF SCompare(format,format)#0 THEN
          Break()
        FI
        header=1
      ELSEIF size=0 THEN
        DecodeSize(line,@width,@height)
        IF width=0 OR height=0 THEN
          Break()
        FI
        img.w=width img.h=height
        size=1
      ELSEIF max=0 THEN
        max=ValB(line)
        IF max#255 THEN
          Break()
        FI
      FI
    FI
  OD
RETURN

PROC LoadPPM6(RgbImage POINTER img CHAR ARRAY path)
  BYTE dev=[1],x,y
  RGB c

  Close(dev)
  Open(dev,path,4)
  LoadHeader(img,"P6",dev)
  FOR y=0 TO img.h-1
  DO
    FOR x=0 TO img.w-1
    DO
      c.r=GetD(dev)
      c.g=GetD(dev)
      c.b=GetD(dev)
      SetRgbPixel(img,x,y,c)
    OD
  OD
  Close(dev)
RETURN

PROC SaveHeader(GrayImage POINTER img
  CHAR ARRAY format BYTE dev)

  PrintDE(dev,format)
  PrintBD(dev,img.w)
  PutD(dev,32)
  PrintBDE(dev,img.h)
  PrintBDE(dev,255)
RETURN

PROC SavePPM2(RgbImage POINTER img CHAR ARRAY path)
  BYTE dev=[1],x,y,c

  Close(dev)
  Open(dev,path,8)
  SaveHeader(img,"P2",dev)
  FOR y=0 TO img.h-1
  DO
    FOR x=0 TO img.w-1
    DO
      c=GetGrayPixel(img,x,y)
      PrintBD(dev,c)
      IF x=img.w-1 THEN
        PutDE(dev)
      ELSE
        PutD(dev,32)
      FI
    OD
  OD
  Close(dev)
RETURN

PROC Load(CHAR ARRAY path)
  CHAR ARRAY line(255)
  BYTE dev=[1]

  Close(dev)
  Open(dev,path,4)
  WHILE Eof(dev)=0
  DO
    InputSD(dev,line)
    PrintE(line)
  OD
  Close(dev)
RETURN

PROC Main()
  BYTE ARRAY rgbdata(300),graydata(100)
  RgbImage rgbimg
  GrayImage grayimg
  CHAR ARRAY path2="D:PPM2.PPM"
  CHAR ARRAY path6="D:PPM6.PPM"

  Put(125) PutE() ;clear the screen
  InitRgbImage(rgbimg,0,0,rgbdata)
  InitRgbToGray()
  
  PrintF("Loading %S...%E%E",path6)
  LoadPPM6(rgbimg,path6)

  PrintF("Converting RGB to grayscale...%E%E")
  InitGrayImage(grayimg,rgbimg.w,rgbimg.h,graydata)
  RgbToGray(rgbimg,grayimg)

  PrintF("Saving %S...%E%E",path2)
  SavePPM2(grayimg,path2)
  PrintF("Loading %S...%E%E",path2)
  Load(path2)
RETURN
Output:

Screenshot from Atari 8-bit computer

Loading D:PPM6.PPM...

Converting RGB to grayscale...

Saving D:PPM2.PPM...

Loading D:PPM2.PPM...

P2
3 4
255
0 18 182
54 201 73
237 255 61
45 54 74

Ada

with Ada.Characters.Latin_1;  use Ada.Characters.Latin_1;
with Ada.Integer_Text_IO;     use Ada.Integer_Text_IO;
with Ada.Streams.Stream_IO;   use Ada.Streams.Stream_IO;

function Get_PPM (File : File_Type) return Image is
   use Ada.Characters.Latin_1;
   use Ada.Integer_Text_IO;

   function Get_Line return String is -- Skips comments
      Byte   : Character;
      Buffer : String (1..80);
   begin
      loop
         for I in Buffer'Range loop
            Character'Read (Stream (File), Byte);
            if Byte = LF then
               exit when Buffer (1) = '#';
               return Buffer (1..I - 1);
            end if;
            Buffer (I) := Byte;
         end loop;
         if Buffer (1) /= '#' then
            raise Data_Error;
         end if;
      end loop;
   end Get_Line;

   Height : Integer;
   Width  : Integer;
begin
   if Get_Line /= "P6" then
      raise Data_Error;
   end if;
   declare
      Line  : String  := Get_Line;
      Start : Integer := Line'First;
      Last  : Positive;
   begin
      Get (Line, Width, Last);                     Start := Start + Last;
      Get (Line (Start..Line'Last), Height, Last); Start := Start + Last;
      if Start <= Line'Last then
         raise Data_Error;
      end if;
      if Width < 1 or else Height < 1 then
         raise Data_Error;
      end if;
   end;
   if Get_Line /= "255" then
      raise Data_Error;
   end if;
   declare
      Result : Image (1..Height, 1..Width);
      Buffer : String (1..Width * 3);
      Index  : Positive;
   begin
      for I in Result'Range (1) loop
         String'Read (Stream (File), Buffer);
         Index := Buffer'First;
         for J in Result'Range (2) loop
            Result (I, J) :=
               (  R => Luminance (Character'Pos (Buffer (Index))),
                  G => Luminance (Character'Pos (Buffer (Index + 1))),
                  B => Luminance (Character'Pos (Buffer (Index + 2)))
               );
            Index := Index + 3;
         end loop;
      end loop;
      return Result;
   end;
end Get_PPM;

The implementation propagates Data_Error when the file format is incorrect. End_Error is propagated when the file end is prematurely met. The following example illustrates conversion of a color file to grayscale.

declare
   F1, F2 : File_Type;
begin
   Open (F1, In_File, "city.ppm");
   Create (F2, Out_File, "city_grayscale.ppm");
   Put_PPM (F2, Color (Grayscale (Get_PPM (F1))));
   Close (F1);
   Close (F2);
end;

ATS

For this you will need the static and dynamic ATS source files of Bitmap#ATS, Grayscale_image#ATS, and Bitmap/Write_a_PPM_file#ATS. (You do not need libnetpbm, although one could easily use it with ATS.)

There are three files here: a static file for the interface to pixmap_read_ppm, a dynamic file for the implementation of pixmap_read_ppm, and a file for the program that converts an image to grayscale. (The last is a dynamic file, but we will call it the program file.)

With pixmap_read_ppm<rgb24> you should be able to read any valid PPM, whether raw or plain, and with any valid Maxval. The result is a pixmap1(rgb24) with implicit Maxval of 255. The reader tries to be very permissive, although there seems not much I can do about the strange way comments work in PPM.

The ATS static file

This file should be called bitmap_read_ppm_task.sats.

#define ATS_PACKNAME "Rosetta_Code.bitmap_read_ppm_task"

staload "bitmap_task.sats"

fn {a : t@ype}
pixmap_read_ppm :
  (* On failure to read, the return is None_vt(). I do not currently
     provide any indication of why the attempt failed, although in
     practice you probably would wish to add that. *)
  FILEref ->
    Option_vt ([w, h : pos] [p : addr | null < p]
               @(mfree_gc_v p | pixmap (a, w, h, p)))

The ATS dynamic file

This file should be called bitmap_read_ppm_task.dats.

(*------------------------------------------------------------------*)

#define ATS_DYNLOADFLAG 0
#define ATS_PACKNAME "Rosetta_Code.bitmap_read_ppm_task"

#include "share/atspre_staload.hats"

staload "bitmap_task.sats"

(* You need to staload bitmap_task.dats, so the ATS compiler will have
   access to its implementations of templates. But we staload it
   anonymously, so the programmer will not have access. *)
staload _ = "bitmap_task.dats"

staload "bitmap_read_ppm_task.sats"

(*------------------------------------------------------------------*)

datavtype magic_number_vt =
| Netpbm_magic_number of int
| Unknown_magic_number of ()

fn {}
read_magic_number (inpf : FILEref) : magic_number_vt =
  let
    val i = fileref_getc inpf
  in
    if i <> char2int0 'P' then
      Unknown_magic_number ()
    else
      let
        val i = fileref_getc inpf
      in
        if i < char2int0 '1' && char2int0 '7' < i then
          Unknown_magic_number ()
        else
          Netpbm_magic_number (i - char2int0 '0')
      end
  end

fn {}
get_next_char (inpf : FILEref) : int =
  let
    fnx
    get_next () : int =
      let
        val i = fileref_getc inpf
      in
        if i = char2int0 '#' then
          skip_through_newline ()
        else
          i
      end
    and
    skip_through_newline () : int =
      let
        val i = fileref_getc inpf
      in
        if i < 0 then
          i
        else if i = char2int0 '\n' then
          get_next ()
        else
          skip_through_newline ()
      end
  in
    get_next ()
  end

(* The only tokens we need to scan for, in P1 through P6, are unsigned
   integers. P7 headers (Portable Arbitrary Map) have a completely
   different arrangement, but we are not handling that. *)
fn {}
get_next_integer (inpf : FILEref)
    (* A negative return value means we have reached the end. We do
       not distinguish whitespace characters from anything else that
       is not a digit or '#'. (Really I want to use intmax_t here,
       rather than llint, but there is no intmax_t support in the
       prelude. The ats2-xprelude package has support, but I am
       avoiding the dependency. *)
    : llint =
  let
    fnx
    look_for_digit () : llint =
      let
        val i = get_next_char inpf
      in
        if i < char2int0 '0' || char2int0 '9' < i then
          look_for_digit ()
        else
          read_digits (g0i2i (i - char2int0 '0'))
      end
    and
    read_digits (x : llint) : llint =
      let
        val i = get_next_char inpf
      in
        if i < char2int0 '0' || char2int0 '9' < i then
          (* I cannot find an "ungetc" in prelude/SATS/filebas.sats,
             so I will use the foreign function interface directly. *)
          let
            typedef FILEstar = $extype"FILE *"
            extern castfn FILEref2star : FILEref -<> FILEstar
          in
            ignoret ($extfcall (int, "ungetc", i, FILEref2star inpf));
            x
          end
        else
          let
            val digit : llint = g0i2i (i - char2int0 '0')
          in
            read_digits ((10LL * x) + digit)
          end
      end
  in
    look_for_digit ()
  end

fn {}
read_ppm_header (inpf : FILEref)
    : Option_vt @(ullint, ullint, ullint) =
  let
    val width = get_next_integer inpf
  in
    if width < 0LL then
      None_vt ()
    else
      let
        val height = get_next_integer inpf
      in
        if height < 0LL then
          None_vt ()
        else
          let
            val maxval = get_next_integer inpf
          in
            if maxval < 0LL then
              None_vt ()
            else
              begin
                (* There is supposed to be a whitespace character (or
                   comments and whitespace character) after the
                   MAXVAL. We will accept anything, whitespace or
                   not. *)
                ignoret (fileref_getc inpf);

                Some_vt @(g0i2u width, g0i2u height, g0i2u maxval)
              end
          end
      end
  end

fn {}
get_next_single_byte (inpf : FILEref) : llint =
  let
    val i = fileref_getc inpf
  in
    if i < 0 then
      ~1LL
    else
      g0i2i i
  end

fn {}
get_next_double_byte (inpf : FILEref) : llint =
  let
    val i1 = fileref_getc inpf
  in
    if i1 < 0 then
      ~1LL
    else
      let
        val i0 = fileref_getc inpf
      in
        if i0 < 0 then
          ~1LL
        else
          let
            val i1 : llint = g0i2i i1
            and i0 : llint = g0i2i i0
          in
            (i1 * 256LL) + i0
          end
      end
  end

(*------------------------------------------------------------------*)
(* Implementation is provided only for rgb24. *)

extern castfn ull2sz : {i : int} ullint i -<> size_t i
extern castfn ull2u : {i : int} ullint i -<> uint i
extern castfn ull2u8 : ullint -<> uint8

extern fn {}
read_raw_ppm_rgb24 : $d2ctype (pixmap_read_ppm<rgb24>)

extern fn {}
read_plain_ppm_rgb24 : $d2ctype (pixmap_read_ppm<rgb24>)

extern fn {}
read_general_ppm_rgb24 : $d2ctype (pixmap_read_ppm<rgb24>)

extern fn {}
read_general$width () : [i : pos] size_t i

extern fn {}
read_general$height () : [i : pos] size_t i

extern fn {}
read_general$maxval () : [i : pos | i <= 65535] uint i

extern fn {}
read_general$next_value : FILEref -> llint

implement
pixmap_read_ppm<rgb24> inpf =
  case+ read_magic_number inpf of
  | ~ Unknown_magic_number () => None_vt ()
  | ~ Netpbm_magic_number num =>
    begin
      case+ num of
      | 6 => read_raw_ppm_rgb24 inpf
      | 3 => read_plain_ppm_rgb24 inpf
      | _ => None_vt
    end

implement {}
read_raw_ppm_rgb24 inpf =
  case+ read_ppm_header inpf of
  | ~ None_vt () => None_vt ()
  | ~ Some_vt @(width, height, maxval) =>
    let
      val width = g1ofg0 width
      and height = g1ofg0 height
      and maxval = g1ofg0 maxval
    in
      if (width < 1LLU) + (height < 1LLU) +
            (maxval < 1LLU) + (65535LLU < maxval) then
        None_vt ()
      else
        let
          val w : Size_t = ull2sz width
          val h : Size_t = ull2sz height
          val maxval : uInt = ull2u maxval
        in
          if maxval = 255u then
            let
              val @(pfgc | pix) = pixmap_make<rgb24> (w, h)
              val success =
                load<rgb24> (inpf, pix, rgb24_make (255, 0, 0))
            in
              if ~success then
                begin
                  free (pfgc | pix);
                  None_vt ()
                end
              else
                Some_vt @(pfgc | pix)
            end
          else if maxval < 256u then
            let
              implement read_general$width<> () = w
              implement read_general$height<> () = h
              implement read_general$maxval<> () = maxval
              implement
              read_general$next_value<> inpf =
                get_next_single_byte inpf
            in
              read_general_ppm_rgb24<> inpf
            end
          else
            let
              implement read_general$width<> () = w
              implement read_general$height<> () = h
              implement read_general$maxval<> () = maxval
              implement
              read_general$next_value<> inpf =
                get_next_double_byte inpf
            in
              read_general_ppm_rgb24<> inpf
            end
        end
    end

implement {}
read_plain_ppm_rgb24 inpf =
  case+ read_ppm_header inpf of
  | ~ None_vt () => None_vt ()
  | ~ Some_vt @(width, height, maxval) =>
    let
      val width = g1ofg0 width
      and height = g1ofg0 height
      and maxval = g1ofg0 maxval
    in
      if (width < 1LLU) + (height < 1LLU) +
            (maxval < 1LLU) + (65535LLU < maxval) then
        None_vt ()
      else
        let
          val w : Size_t = ull2sz width
          val h : Size_t = ull2sz height
          val maxval : uInt = ull2u maxval
          implement read_general$width<> () = w
          implement read_general$height<> () = h
          implement read_general$maxval<> () = maxval
          implement
            read_general$next_value<> inpf =
              get_next_integer inpf
        in
          read_general_ppm_rgb24<> inpf
        end
    end

implement {}
read_general_ppm_rgb24 inpf =
  let
    val [w : int] w = read_general$width<> ()
    and [h : int] h = read_general$height<> ()
    and maxval = read_general$maxval<> ()

    fn
    scale_value (v : ullint) : uint8 =
      if maxval = 255u then
        ull2u8 v
      else
        let
          val maxval : ullint = g0u2u maxval
          val v = 255LLU * v
          val v1 = v / maxval
          and v0 = v mod maxval
        in
          if v0 + v0 < maxval then
            ull2u8 v1
          else if maxval < v0 + v0 then
            ull2u8 (succ v1)
          else if v1 mod 2LLU = 0LLU then
            ull2u8 v1
          else
            ull2u8 (succ v1)
        end

    (* For easier programming, start with a fully initialized
       pixmap. The routine probably is I/O-bound, anyway. *)
    val @(pfgc | pix) =
      pixmap_make<rgb24> (w, h, rgb24_make (255, 0, 0))

    macdef between (i, j, v) =
      let
        val v = ,(v)
      in
        (,(i) <= v) * (v <= ,(j))
      end

    fun
    loop {x, y : nat | x <= w; y <= h}
         .<h - y, w - x>.
         (pix : !pixmap (rgb24, w, h),
          x   : size_t x,
          y   : size_t y)
        : bool (* success *) =
      if y = h then
        true
      else if x = w then
        loop (pix, i2sz 0, succ y)
      else
        let
          val maxv : llint = g0u2i maxval
          val vr = read_general$next_value<> inpf
        in
          if ~between (0LL, maxv, vr) then
            false
          else
            let
              val vg = read_general$next_value<> inpf
            in
              if ~between (0LL, maxv, vg) then
                false
              else
                let
                  val vb = read_general$next_value<> inpf
                in
                  if ~between (0LL, maxv, vb) then
                    false
                  else
                    let
                      val r = scale_value (g0i2u vr)
                      and g = scale_value (g0i2u vg)
                      and b = scale_value (g0i2u vb)
                    in
                      pix[x, y] := rgb24_make @(r, g, b);
                      loop (pix, succ x, y)
                    end
                end
            end
        end

    val success = loop (pix, i2sz 0, i2sz 0)
  in
    if ~success then
      begin
        free (pfgc | pix);
        None_vt ()
      end
    else
      Some_vt @(pfgc | pix)
  end

(*------------------------------------------------------------------*)

#ifdef BITMAP_READ_PPM_TASK_TEST #then

staload "bitmap_write_ppm_task.sats"
staload _ = "bitmap_write_ppm_task.dats"

(* The test program converts a PPM at standard input to a raw PPM with
   MAXVAL 255. *)
implement
main0 () =
  let
    val pix_opt = pixmap_read_ppm<rgb24> stdin_ref
  in
    case+ pix_opt of
    | ~ None_vt () => ()
    | ~ Some_vt @(pfgc | pix) =>
      begin
        ignoret (pixmap_write_ppm (stdout_ref, pix));
        free (pfgc | pix)
      end
  end

#endif

(*------------------------------------------------------------------*)

The ATS program file

This file should be called bitmap_read_ppm_task_program.dats (though it actually could be called by another name).

A gnarly tree on a rise by the sea, in color.
A gnarly tree on a rise by the sea, in grayscale.
(* The program should be able to read a PPM in raw or plain format,
   with any valid Maxval. The output will be a grayscale raw PPM with
   Maxval=255.

   Compile with "myatscc bitmap_read_ppm_task_program.dats", which
   should give you a program named "bitmap_read_ppm_task_program". *)

(*

##myatsccdef=\
patscc -std=gnu2x -g -O2 -DATS_MEMALLOC_LIBC \
  -o $fname($1) $1 \
  bitmap{,_{{read,write}_ppm,grayscale}}_task.{s,d}ats

*)

#include "share/atspre_staload.hats"

staload "bitmap_task.sats"
staload "bitmap_read_ppm_task.sats"
staload "bitmap_write_ppm_task.sats"
staload "bitmap_grayscale_task.sats"

staload _ = "bitmap_task.dats"
staload _ = "bitmap_read_ppm_task.dats"
staload _ = "bitmap_write_ppm_task.dats"
staload _ = "bitmap_grayscale_task.dats"

implement
main0 (argc, argv) =
  let
    val args = listize_argc_argv (argc, argv)
    val nargs = length args

    val inpf =
      if nargs < 2 then
        stdin_ref
      else if args[1] = "-" then
        stdin_ref
      else
        fileref_open_exn (args[1], file_mode_r)
    val pix_opt = pixmap_read_ppm<rgb24> inpf
    val () = fileref_close inpf
  in
    case+ pix_opt of
    | ~ None_vt () =>
      begin
        free args;
        println! ("For some reason, I failed to read the image.");
        exit 1
      end
    | ~ Some_vt @(pfgc1 | pix1) =>
      let
        val @(pfgc2 | pix2) = pixmap_convert<rgb24,gray8> pix1
        val () = free (pfgc1 | pix1)
        val @(pfgc3 | pix3) = pixmap_convert<gray8,rgb24> pix2
        val () = free (pfgc2 | pix2)

        val outf =
          if nargs < 3 then
            stdout_ref
          else if args[2] = "-" then
            stdout_ref
          else
            fileref_open_exn (args[2], file_mode_w)
        val success = pixmap_write_ppm<rgb24> (outf, pix3)
        val () = fileref_close outf

        val () = free (pfgc3 | pix3)
      in
        free args;
        if ~success then
          begin
            println! ("For some reason, ",
                      "I failed to write a new image.");
            exit 2
          end
      end
  end

You can compile the program with the shell command

myatscc bitmap_read_ppm_task_program.dats

If compilation is successful, the program will be called bitmap_read_ppm_task_program. You can give up to two arguments (any others will be ignored). The first argument is a file name for the input file, the second is the file name for the output file. Either argument can be "-", meaning to use the respective standard input or output. An argument omitted is equivalent to "-".

Shown in the margin are before and after for SIPI test image 4.1.06 (not counting that I have converted the PPM files to JPEGs).

AutoHotkey

Works with: AutoHotkey_L

Only ppm6 files supported.

img := ppm_read("lena50.ppm") ;   
x := img[4,4] ; get pixel(4,4)
y := img[24,24] ; get pixel(24,24)
msgbox % x.rgb() " " y.rgb()
img.write("lena50copy.ppm")
return
 
ppm_read(filename, ppmo=0) ; only ppm6 files supported 
{
if !ppmo  ; if image not already in memory, read from filename
  fileread, ppmo, % filename 

  index := 1  
  pos := 1

  loop, parse, ppmo, `n, `r
  {
    if (substr(A_LoopField, 1, 1) == "#")
      continue
loop, 
{ 
 if !pos := regexmatch(ppmo, "\d+", pixel, pos)
break
    bitmap%A_Index% := pixel
    if (index == 4)
      Break
    pos := regexmatch(ppmo, "\s", x, pos)
    index ++
}
  }
 
  type := bitmap1
  width := bitmap2
  height := bitmap3
  maxcolor := bitmap4
  bitmap := Bitmap(width, height, color(0,0,0))
  index := 1
  i := 1
  j := 1
 bits := pos 
loop % width * height 
  {
      bitmap[i, j, "r"]  := numget(ppmo, 3 * A_Index + bits, "uchar")
      bitmap[i, j, "g"]  := numget(ppmo, 3 * A_Index + bits + 1, "uchar")
      bitmap[i, j, "b"]  := numget(ppmo, 3 * A_Index + bits + 2, "uchar")

      if (j == width)
{
	j := 1
	i += 1
}
      else
	j++
}
 return bitmap  
  }
#include bitmap_storage.ahk ; from http://rosettacode.org/wiki/Basic_bitmap_storage/AutoHotkey

BBC BASIC

      f% = OPENIN("c:\lena.ppm")
      IF f%=0 ERROR 100, "Failed to open input file"
      
      IF GET$#f% <> "P6" ERROR 101, "File is not in P6 format"
      REPEAT
        in$ = GET$#f%
      UNTIL LEFT$(in$,1) <> "#"
      size$ = in$
      max$ = GET$#f%
      
      Width% = VAL(size$)
      space% = INSTR(size$, " ")
      Height% = VALMID$(size$, space%)
      
      VDU 23,22,Width%;Height%;8,16,16,128
      
      FOR y% = Height%-1 TO 0 STEP -1
        FOR x% = 0 TO Width%-1
          r% = BGET#f% : g% = BGET#f% : b% = BGET#f%
          l% = INT(0.3*r% + 0.59*g% + 0.11*b% + 0.5)
          PROCsetpixel(x%,y%,l%,l%,l%)
        NEXT
      NEXT y%
      END
      
      DEF PROCsetpixel(x%,y%,r%,g%,b%)
      COLOUR 1,r%,g%,b%
      GCOL 1
      LINE x%*2,y%*2,x%*2,y%*2
      ENDPROC

C

It is up to the caller to open the file and pass the handler to the function. So this code can be used in Read image file through a pipe without modification. It only understands the P6 file format.

Interface:

image get_ppm(FILE *pf);

Implementation:

#include "imglib.h"

#define PPMREADBUFLEN 256
image get_ppm(FILE *pf)
{
        char buf[PPMREADBUFLEN], *t;
        image img;
        unsigned int w, h, d;
        int r;
        
        if (pf == NULL) return NULL;
        t = fgets(buf, PPMREADBUFLEN, pf);
        /* the code fails if the white space following "P6" is not '\n' */
        if ( (t == NULL) || ( strncmp(buf, "P6\n", 3) != 0 ) ) return NULL;
        do
        { /* Px formats can have # comments after first line */
           t = fgets(buf, PPMREADBUFLEN, pf);
           if ( t == NULL ) return NULL;
        } while ( strncmp(buf, "#", 1) == 0 );
        r = sscanf(buf, "%u %u", &w, &h);
        if ( r < 2 ) return NULL;

        r = fscanf(pf, "%u", &d);
        if ( (r < 1) || ( d != 255 ) ) return NULL;
        fseek(pf, 1, SEEK_CUR); /* skip one byte, should be whitespace */

        img = alloc_img(w, h);
        if ( img != NULL )
        {
            size_t rd = fread(img->buf, sizeof(pixel), w*h, pf);
            if ( rd < w*h )
            {
               free_img(img);
               return NULL;
            }
            return img;
        }
}

The following acts as a filter to convert a PPM file read from standard input into a PPM gray image, and it outputs the converted image to standard output (see Grayscale image, Write ppm file, and Raster graphics operations in general):

#include <stdio.h>
#include "imglib.h"

int main()
{
   image source;
   grayimage idest;
   
   source = get_ppm(stdin);
   idest = tograyscale(source);
   free_img(source);
   source = tocolor(idest);
   output_ppm(stdout, source);
   free_img(source); free_img((image)idest);
   return 0;
}

C#

Tested with this solution.

using System.IO;
class PPMReader
{
    public static Bitmap ReadBitmapFromPPM(string file)
    {
        var reader = new BinaryReader(new FileStream(file, FileMode.Open));
        if (reader.ReadChar() != 'P' || reader.ReadChar() != '6')
            return null;
        reader.ReadChar(); //Eat newline
        string widths = "", heights = "";
        char temp;
        while ((temp = reader.ReadChar()) != ' ')
            widths += temp;
        while ((temp = reader.ReadChar()) >= '0' && temp <= '9')
            heights += temp;
        if (reader.ReadChar() != '2' || reader.ReadChar() != '5' || reader.ReadChar() != '5')
            return null;
        reader.ReadChar(); //Eat the last newline
        int width = int.Parse(widths),
            height = int.Parse(heights);
        Bitmap bitmap = new Bitmap(width, height);
        //Read in the pixels
        for (int y = 0; y < height; y++)
            for (int x = 0; x < width; x++)
                bitmap.SetPixel(x, y, new Bitmap.Color()
                {
                    Red = reader.ReadByte(),
                    Green = reader.ReadByte(),
                    Blue = reader.ReadByte()
                });
        return bitmap;
    }
}

Common Lisp

The function read-ppm-image reads either a P6 or P3 file depending on the file contents. The package description assumes that you have the Basic bitmap storage#Common Lisp package.

(in-package #:rgb-pixel-buffer)

(defparameter *whitespaces-chars* '(#\SPACE #\RETURN #\TAB #\NEWLINE #\LINEFEED))

(defun read-header-chars (stream &optional (delimiter-list *whitespaces-chars*))
  (do ((c (read-char stream nil :eof)
          (read-char stream nil :eof))
       (vals nil (if (or (null c) (char= c  #\#)) vals (cons c vals))))   ;;don't collect comment chars
       ((or (eql c :eof) (member c delimiter-list)) (map 'string #'identity (nreverse vals)))   ;;return strings
    (when (char= c #\#)   ;;skip comments
      (read-line stream))))

(defun read-ppm-file-header (file)
  (with-open-file (s file :direction :input)
    (do ((failure-count 0 (1+ failure-count))
	 (tokens nil (let ((t1 (read-header-chars s)))
		       (if (> (length t1) 0)
			   (cons t1 tokens)
			   tokens))))
	((>= (length tokens) 4) (values (nreverse tokens)
			      (file-position s)))
      (when (>= failure-count 10)
	(error (format nil "File ~a does not seem to be a proper ppm file - maybe too many comment lines" file)))
      (when (= (length tokens) 1)
	(when (not (or (string= (first tokens) "P6") (string= (first tokens) "P3")))
	  (error (format nil "File ~a is not a ppm file - wrong magic-number. Read ~a instead of P6 or P3 " file (first tokens))))))))

(defun read-ppm-image (file)
  (flet ((image-data-reader (stream start-position width height image-build-function read-function)
	   (file-position stream start-position)
	   (dotimes (row height)
	     (dotimes (col width)
	       (funcall image-build-function row col (funcall read-function stream))))))
    (multiple-value-bind (header file-pos) (read-ppm-file-header file)
      (let* ((image-type (first header))
	     (width (parse-integer (second header) :junk-allowed t))
	     (height (parse-integer (third header) :junk-allowed t))
	     (max-value (parse-integer (fourth header) :junk-allowed t))
	     (image (make-rgb-pixel-buffer width height)))
	(when (> max-value 255)
	  (error "unsupported depth - convert to 1byte depth with pamdepth"))
	(cond ((string= "P6" image-type)
	       (with-open-file (stream file :direction :input :element-type '(unsigned-byte 8))
		 (image-data-reader stream
				    file-pos
				    width
				    height
				    #'(lambda (w h val)
					(setf (rgb-pixel image w h) val))
				    #'(lambda (stream)
					(make-rgb-pixel (read-byte stream)
							(read-byte stream)
							(read-byte stream))))
		 image))
	      ((string= "P3" image-type)
	       (with-open-file (stream file :direction :input)
		 (image-data-reader stream
				    file-pos
				    width
				    height
				    #'(lambda (w h val)
					(setf (rgb-pixel image w h) val))
				    #'(lambda (stream)
					(make-rgb-pixel (read stream)
							(read stream)
							(read stream))))
		 image))
	      (t 'unsupported))
      image))))

(export 'read-ppm-image)

To read the feep.ppm file as shown on the description page for the ppm format use:

(read-ppm-image "feep.ppm")

D

The Image module contains a loadPPM6 function to load binary PPM images.

Delphi

Class helper for read and write Bitmap's and Ppm's

Translation of: C#
program BtmAndPpm;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils,
  System.Classes,
  Winapi.Windows,
  Vcl.Graphics;

type
  TBitmapHelper = class helper for TBitmap
  private
  public
    procedure SaveAsPPM(FileName: TFileName; useGrayScale: Boolean = False);
    procedure LoadFromPPM(FileName: TFileName; useGrayScale: Boolean = False);
  end;

function ColorToGray(Color: TColor): TColor;
var
  L: Byte;
begin
  L := round(0.2126 * GetRValue(Color) + 0.7152 * GetGValue(Color) + 0.0722 *
    GetBValue(Color));
  Result := RGB(L, L, L);
end;

{ TBitmapHelper }

procedure TBitmapHelper.SaveAsPPM(FileName: TFileName; useGrayScale: Boolean = False);
var
  i, j, color: Integer;
  Header: AnsiString;
  ppm: TMemoryStream;
begin
  ppm := TMemoryStream.Create;
  try
    Header := Format('P6'#10'%d %d'#10'255'#10, [Self.Width, Self.Height]);
    writeln(Header);
    ppm.Write(Tbytes(Header), Length(Header));

    for i := 0 to Self.Height - 1 do
      for j := 0 to Self.Width - 1 do
      begin
        if useGrayScale then
          color := ColorToGray(ColorToRGB(Self.Canvas.Pixels[i, j]))
        else
          color := ColorToRGB(Self.Canvas.Pixels[i, j]);
        ppm.Write(color, 3);
      end;
    ppm.SaveToFile(FileName);
  finally
    ppm.Free;
  end;
end;

procedure TBitmapHelper.LoadFromPPM(FileName: TFileName; useGrayScale: Boolean = False);
var
  p: Integer;
  ppm: TMemoryStream;
  sW, sH: string;
  temp: AnsiChar;
  W, H: Integer;
  Color: TColor;

  function ReadChar: AnsiChar;
  begin
    ppm.Read(Result, 1);
  end;

begin
  ppm := TMemoryStream.Create;
  ppm.LoadFromFile(FileName);
  if ReadChar + ReadChar <> 'P6' then
    exit;

  repeat
    temp := ReadChar;
    if temp in ['0'..'9'] then
      sW := sW + temp;
  until temp = ' ';

  repeat
    temp := ReadChar;
    if temp in ['0'..'9'] then
      sH := sH + temp;
  until temp = #10;

  W := StrToInt(sW);
  H := StrToInt(sH);

  if ReadChar + ReadChar + ReadChar <> '255' then
    exit;

  ReadChar(); //skip newLine

  SetSize(W, H);
  p := 0;
  while ppm.Read(Color, 3) > 0 do
  begin
    if useGrayScale then
      Color := ColorToGray(Color);
    Canvas.Pixels[p mod W, p div W] := Color;
    inc(p);
  end;
  ppm.Free;
end;

begin
  with TBitmap.Create do
  begin
    // Load bmp
    LoadFromFile('Input.bmp');
    // Save as ppm
    SaveAsPPM('Output.ppm');

    // Load as ppm and convert in grayscale
    LoadFromPPM('Output.ppm', True);

    // Save as bmp
    SaveToFile('Output.bmp');

    Free;
  end;
end.

E

def chr := <import:java.lang.makeCharacter>.asChar

def readPPM(inputStream) {
  # Proper native-to-E stream IO facilities have not been designed and
  # implemented yet, so we are borrowing Java's. Poorly. This *will* be
  # improved eventually.
  
  # Reads one header token, skipping comments and whitespace, and exactly
  # one trailing whitespace character
  def readToken() {
    var token := ""
    var c := chr(inputStream.read())
    while (c == ' ' || c == '\t' || c == '\r' || c == '\n' || c == '#') {
      if (c == '#') {
        while (c != '\n') { c := chr(inputStream.read()) }
      }
      # skip over initial whitespace
      c := chr(inputStream.read())
    }
    while (!(c == ' ' || c == '\t' || c == '\r' || c == '\n')) {
      if (c == '#') {
        while (c != '\n') { c := chr(inputStream.read()) }
      } else {
        token += E.toString(c)
        c := chr(inputStream.read())
      }
    }
    return token
  }

  # Header
  require(readToken() == "P6")
  def width := __makeInt(readToken())
  def height := __makeInt(readToken())
  def maxval := __makeInt(readToken())

  def size := width * height * 3

  # Body
  # See [[Basic bitmap storage]] for the definition and origin of sign()
  def data := <elib:tables.makeFlexList>.fromType(<type:java.lang.Byte>, size)
  if (maxval >= 256) {
    for _ in 1..size {
      data.push(sign((inputStream.read() * 256 + inputStream.read()) * 255 // maxval))
    }
  } else {
    for _ in 1..size {
      data.push(sign(inputStream.read() * 255 // maxval))
    }
  }

  def image := makeImage(width, height)
  image.replace(data.snapshot())
  return image
}

Note: As of this writing the grayscale image task has not been implemented, so the task code (below) won't actually run yet. But readPPM above has been tested separately.

def readPPMTask(inputFile, outputFile) {
  makeGrayscale \
    .fromColor(readPPM(<import:java.io.makeFileInputStream>(inputFile))) \
    .toColor() \
    .writePPM(<import:java.io.makeFileOutputStream>(outputFile))
}

Erlang

% This module provides basic operations on ppm files:
% Read from file, create ppm in memory (from generic bitmap) and save to file.
% Writing PPM files was introduced in roseta code task 'Bitmap/Write a PPM file'
% but the same code is included here to provide whole set of operations on ppm
% needed for purposes of this task.

-module(ppm).

-export([ppm/1, write/2, read/1]).

% constants for writing ppm file
-define(WHITESPACE, <<10>>).
-define(SPACE, <<32>>).

% constants for reading ppm file
-define(WHITESPACES, [9, 10, 13, 32]).
-define(PPM_HEADER, "P6").

% data structure introduced in task Bitmap (module ros_bitmap.erl)
-record(bitmap, {
    mode = rgb,
    pixels = nil,
    shape = {0, 0}
  }).

%%%%%%%%% API %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% read ppm file from file
read(Filename) ->
    {ok, File} = file:read_file(Filename),
    parse(File).

% create ppm image from bitmap record
ppm(Bitmap) ->
    {Width, Height} = Bitmap#bitmap.shape,
    Pixels = ppm_pixels(Bitmap),
    Maxval = 255,  % original ppm format maximum
    list_to_binary([
      header(), width_and_height(Width, Height), maxval(Maxval), Pixels]).

% write bitmap as ppm file
write(Bitmap, Filename) ->
    Ppm = ppm(Bitmap),
    {ok, File} = file:open(Filename, [binary, write]),
    file:write(File, Ppm),
    file:close(File).

%%%%%%%%% Reading PPM %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
parse(Binary) ->
    {?PPM_HEADER, Data} = get_next_token(Binary),
    {Width, HeightAndRest} = get_next_token(Data),
    {Height, MaxValAndRest} = get_next_token(HeightAndRest),
    {_MaxVal, RawPixels} = get_next_token(MaxValAndRest),
    Shape = {list_to_integer(Width), list_to_integer(Height)},
    Pixels = load_pixels(RawPixels),
    #bitmap{pixels=Pixels, shape=Shape}.

% load binary as a list of RGB triplets
load_pixels(Binary) when is_binary(Binary)->
    load_pixels([], Binary).
load_pixels(Acc, <<>>) ->
    array:from_list(lists:reverse(Acc));
load_pixels(Acc, <<R, G, B, Rest/binary>>) ->
    load_pixels([<<R,G,B>>|Acc], Rest).

is_whitespace(Byte) ->
    lists:member(Byte, ?WHITESPACES).

% get next part of PPM file, skip whitespaces, and return the rest of a binary
get_next_token(Binary) ->
    get_next_token("", true, Binary).
get_next_token(CurrentToken, false, <<Byte, Rest/binary>>) ->
    case is_whitespace(Byte) of
        true ->
            {lists:reverse(CurrentToken), Rest};
        false ->
            get_next_token([Byte | CurrentToken], false, Rest)
    end;
get_next_token(CurrentToken, true, <<Byte, Rest/binary>>) ->
    case is_whitespace(Byte) of
        true ->
            get_next_token(CurrentToken, true, Rest);
        false ->
            get_next_token([Byte | CurrentToken], false, Rest)
    end.

%%%%%%%%% Writing PPM %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
header() ->
    [<<"P6">>, ?WHITESPACE].

width_and_height(Width, Height) ->
    [encode_decimal(Width), ?SPACE, encode_decimal(Height), ?WHITESPACE].

maxval(Maxval) ->
   [encode_decimal(Maxval), ?WHITESPACE].

ppm_pixels(Bitmap) ->
    % 24 bit color depth
    array:to_list(Bitmap#bitmap.pixels).

encode_decimal(Number) ->
    integer_to_list(Number).

Usage in accordance with Grayscale Task:

Colorful = ppm:read("colorful.ppm"),
Gray = ros_bitmap:convert(ros_bitmap:convert(Colorful, grey), rgb),
ppm:write(Gray, "gray.ppm"),

Euphoria

include get.e

function get2(integer fn)
    sequence temp
    temp = get(fn)
    return temp[2] - temp[1]*temp[1]
end function

function read_ppm(sequence filename)
    sequence image, line
    integer dimx, dimy, maxcolor
    atom fn
    fn = open(filename, "rb")
    if fn < 0 then
        return -1 -- unable to open
    end if
    line = gets(fn)
    if not equal(line,"P6\n") then
        return -1 -- only ppm6 files are supported
    end if
    dimx = get2(fn)
    if dimx < 0 then
        return -1
    end if
    dimy = get2(fn)
    if dimy < 0 then
        return -1
    end if
    maxcolor = get2(fn)
    if maxcolor != 255 then
        return -1 -- maxcolors other then 255 are not supported
    end if
    image = repeat(repeat(0,dimy),dimx)
    for y = 1 to dimy do
        for x = 1 to dimx do
            image[x][y] = getc(fn)*#10000 + getc(fn)*#100 + getc(fn)
        end for
    end for
    close(fn)
    return image
end function

Converting an image to grayscale:

sequence image
image = read_ppm("image.ppm")
image = to_gray(image)
image = to_color(image)
write_ppm("image_gray.ppm",image)

FBSL

Read a colored PPM file, convert it to grayscale and write back to disk under a different name. Sanity checks are omitted for brevity.

24-bpp P6 PPM solution:

#ESCAPECHARS ON

DIM colored = ".\\Lena.ppm", grayscale = ".\\LenaGry.ppm"
DIM head, tail, r, g, b, l, ptr, blobsize

FILEGET(FILEOPEN(colored, BINARY), FILELEN(colored)): FILECLOSE(FILEOPEN) ' Load buffer
blobsize = INSTR(FILEGET, "\n255\n") + 4 ' Get sizeof PPM header
head = @FILEGET + blobsize: tail = @FILEGET + FILELEN ' Set loop bounds

FOR ptr = head TO tail STEP 3 ' Transform color triplets
	r = PEEK(ptr + 0, 1) ' Read colors stored in RGB order
	g = PEEK(ptr + 1, 1)
	b = PEEK(ptr + 2, 1)
	l = 0.2126 * r + 0.7152 * g + 0.0722 * b ' Derive luminance
	POKE(ptr + 0, CHR(l))(ptr + 1, CHR)(ptr + 2, CHR) ' Write grayscale
NEXT

FILEPUT(FILEOPEN(grayscale, BINARY_NEW), FILEGET): FILECLOSE(FILEOPEN) ' Save buffer

Forth

: read-ppm { fid -- bmp }
  pad dup 80 fid read-line throw 0= abort" Partial line"
  s" P6" compare abort" Only P6 supported."
  pad dup 80 fid read-line throw 0= abort" Partial line"
  0. 2swap >number
  1 /string		\ skip space
  0. 2swap >number
  2drop drop nip    ( w h )
  bitmap { bmp }
  pad dup 80 fid read-line throw 0= abort" Partial line"
  s" 255" compare abort" Only 8-bits per color channel supported"
  0 pad !
  bmp bdim
  0 do
    dup 0 do
      pad 3 fid read-file throw
      3 - abort" Not enough pixel data in file"
      pad @ i j bmp b!
    loop
  loop drop
  bmp ;

\ testing round-trip
4 3 bitmap value test
red test bfill
green 1 2 test b!

s" red.ppm" w/o create-file throw
test over write-ppm
close-file throw

s" red.ppm" r/o open-file throw
dup read-ppm value test2
close-file throw

: bsize ( bmp -- len ) bdim * pixels bdata ;

test dup bsize  test2 dup bsize  compare .    \ 0 if identical

Fortran

Works with: Fortran version 90 and later

(This function is part of module RCImageIO, see Write ppm file)

subroutine read_ppm(u, img) 
  integer, intent(in) :: u
  type(rgbimage), intent(out) :: img
  integer :: i, j, ncol, cc
  character(2) :: sign
  character :: ccode
  
  img%width = 0
  img%height = 0
  nullify(img%red)
  nullify(img%green)
  nullify(img%blue)

  read(u, '(A2)') sign
  read(u, *) img%width, img%height
  read(u, *) ncol

  write(0,*) sign
  write(0,*) img%width, img%height
  write(0,*) ncol

  if ( ncol /= 255 ) return

  call alloc_img(img, img%width, img%height)

  if ( valid_image(img) ) then
     do j=1, img%height
        do i=1, img%width
           read(u, '(A1)', advance='no', iostat=status) ccode
           cc = iachar(ccode)
           img%red(i,j) = cc
           read(u, '(A1)', advance='no', iostat=status) ccode
           cc = iachar(ccode)
           img%green(i,j) = cc
           read(u, '(A1)', advance='no', iostat=status) ccode
           cc = iachar(ccode)
           img%blue(i,j) = cc
        end do
     end do
  end if

end subroutine read_ppm

Notes:

  • doing formatted I/O with Fortran is a pain... And unformatted does not mean free; Fortran2003 has streams, but they are not implemented (yet) in GNU Fortran compiler. Here (as in the write part) I've tried to handle the PPM format through formatted I/O. The tests worked but I have not tried still everything.
  • comments after the first line are not handled

FreeBASIC

Translation of: Yabasic
Dim As String imagen = "Lena.ppm"

Sub readPPM (fs As String)
    Dim As Integer x, y, ancho, alto
    Dim As String t, kolor
    Dim As Ubyte r, g, b
    
    If Len(fs) = 0 Then Print "No PPM file name indicated.": Exit Sub
    
    Dim As Long ff = Freefile
    Open fs For Binary As #ff
    If Err Then Print "File "; fs; " not found.": Exit Sub
    
    Input #ff, t, ancho, alto, kolor
    
    If t = "P6" Then
        Screenres ancho, alto, 32
        For y = 0 To alto - 1
            For x = 0 To ancho - 1
                Get #ff, , r
                Get #ff, , g
                Get #ff, , b
                Pset (x, y), Rgb(r, g, b)
            Next x
        Next y
        Close #ff
    Else
        Print "File is NOT PPM P6 type."
    End If
End Sub

readPPM(imagen)
Sleep

Go

package raster

import (
    "errors"
    "io"
    "io/ioutil"
    "os"
    "regexp"
    "strconv"
)

// ReadFrom constructs a Bitmap object from an io.Reader.
func ReadPpmFrom(r io.Reader) (b *Bitmap, err error) {
    var all []byte
    all, err = ioutil.ReadAll(r)
    if err != nil {
        return
    }
    bss := rxHeader.FindSubmatch(all)
    if bss == nil {
        return nil, errors.New("unrecognized ppm header")
    }
    x, _ := strconv.Atoi(string(bss[3]))
    y, _ := strconv.Atoi(string(bss[6]))
    maxval, _ := strconv.Atoi(string(bss[9]))
    if maxval > 255 {
        return nil, errors.New("16 bit ppm not supported")
    }
    allCmts := append(append(append(bss[1], bss[4]...), bss[7]...), bss[10]...)
    b = NewBitmap(x, y)
    b.Comments = rxComment.FindAllString(string(allCmts), -1)
    b3 := all[len(bss[0]):]
    var n1 int
    for i := range b.px {
        b.px[i].R = byte(int(b3[n1]) * 255 / maxval)
        b.px[i].G = byte(int(b3[n1+1]) * 255 / maxval)
        b.px[i].B = byte(int(b3[n1+2]) * 255 / maxval)
        n1 += 3
    }
    return
}

const (
    // single whitespace character
    ws = "[ \n\r\t\v\f]"
    // isolated comment
    cmt = "#[^\n\r]*"
    // comment sub expression
    cmts = "(" + ws + "*" + cmt + "[\n\r])"
    // number with leading comments
    num = "(" + cmts + "+" + ws + "*|" + ws + "+)([0-9]+)"
)

var rxHeader = regexp.MustCompile("^P6" + num + num + num +
    "(" + cmts + "*" + ")" + ws)
var rxComment = regexp.MustCompile(cmt)

// ReadFile writes binary P6 format PPM from the specified filename.
func ReadPpmFile(fn string) (b *Bitmap, err error) {
    var f *os.File
    if f, err = os.Open(fn); err != nil {
        return
    }
    if b, err = ReadPpmFrom(f); err != nil {
        return
    }
    return b, f.Close()
}

Demonstration program, also demonstrating functions from task Grayscale image:

package main

// Files required to build supporting package raster are found in:
// * This task (immediately above)
// * Bitmap
// * Grayscale image
// * Write a PPM file

import (
    "raster"
    "fmt"
)

func main() {
    // (A file with this name is output by the Go solution to the task
    // "Bitmap/Read an image through a pipe," but of course any 8-bit
    //  P6 PPM file should work.)
    b, err := raster.ReadPpmFile("pipein.ppm")
    if err != nil {
        fmt.Println(err)
        return
    }
    b = b.Grmap().Bitmap()
    err = b.WritePpmFile("grayscale.ppm")
    if err != nil {
        fmt.Println(err)
    }
}

Haskell

The definition of Bitmap.Netpbm.readNetpbm is given here.

import Bitmap
import Bitmap.RGB
import Bitmap.Gray
import Bitmap.Netpbm

import Control.Monad
import Control.Monad.ST

main = 
    (readNetpbm "original.ppm" :: IO (Image RealWorld RGB)) >>=
    stToIO . toGrayImage >>=
    writeNetpbm "new.pgm"

The above writes a PGM, not a PPM, since the image being output is in grayscale. If you actually want a gray PPM, convert the Image RealWorld Gray back to an Image RealWorld RGB first:

main =
    (readNetpbm "original.ppm" :: IO (Image RealWorld RGB)) >>=
    stToIO . (toRGBImage <=< toGrayImage) >>=
    writeNetpbm "new.ppm"

J

Solution:
Uses makeRGB from Basic bitmap storage.

require 'files'

readppm=: monad define
  dat=. fread y                                           NB. read from file
  msk=. 1 ,~ (*. 3 >: +/\) (LF&=@}: *. '#'&~:@}.) dat     NB. mark field ends
  't wbyh maxval dat'=. msk <;._2 dat                     NB. parse
  'wbyh maxval'=. 2 1([ {. [: _99&". (LF,' ')&charsub)&.> wbyh;maxval  NB. convert to numeric
  if. (_99 0 +./@e. wbyh,maxval) +. 'P6' -.@-: 2{.t do. _1 return. end.
  (a. i. dat) makeRGB |.wbyh                              NB. convert to basic bitmap format
)

Example:
Using utilities and file from Grayscale image and Write ppm file.
Writes a gray PPM file (a color format) which is bigger than necessary. A PGM file would be more appropriate.

myimg=: readppm jpath '~temp/myimg.ppm'
myimgGray=: toColor toGray myimg
myimgGray writeppm jpath '~temp/myimgGray.ppm'

Java

For convenience, the code for the class used in the Bitmap task here and integrated with the code in the Grayscale image is included.

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.awt.image.RenderedImage;
import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

import javax.imageio.ImageIO;

public class ReadPPMFile {

	public static void main(String[] aArgs) throws IOException {
        // Using the file created in the Bitmap task
		String filePath = "output.ppm";
		
		reader = new BufferedInputStream( new FileInputStream(filePath) );
		final char header1 = (char) reader.read();
        final char header2 = (char) reader.read();
        final char header3 = (char) reader.read();
        if ( header1 != 'P' || header2 != '6' || header3 != END_OF_LINE) {
        	reader.close();
        	throw new IllegalArgumentException("Not a valid P6 PPM file");
        }
        
        final int width = processCharacters(SPACE_CHARACTER);  
        final int height = processCharacters(END_OF_LINE);
        final int maxColorValue = processCharacters(END_OF_LINE);
        if ( maxColorValue < 0 || maxColorValue > 255 ) {
        	reader.close();
        	throw new IllegalArgumentException("Maximum color value is outside the range 0..255");
        }            
        
        // Remove any comments before reading data
        reader.mark(1);
        while ( reader.read() == START_OF_COMMENT ) {
        	 while ( reader.read() != END_OF_LINE );
        	 reader.mark(1);
        }
        reader.reset();
                
       // Read data
        BasicBitmapStorage bitmap = new BasicBitmapStorage(width, height);
        
        byte[] buffer = new byte[width * 3];
        for ( int y = 0; y < height; y++ ) {
            reader.read(buffer, 0, buffer.length);
            for ( int x = 0; x < width; x++ ) {                	
                Color color = new Color(Byte.toUnsignedInt(buffer[x * 3]),
                						Byte.toUnsignedInt(buffer[x * 3 + 1]),
                						Byte.toUnsignedInt(buffer[x * 3 + 2]));
                bitmap.setPixel(x, y, color);
            }
        }
        
        reader.close();
        
        // Convert to gray scale and save to a file
        bitmap.convertToGrayscale();
        File grayFile = new File("outputGray.jpg");
        ImageIO.write((RenderedImage) bitmap.getImage(), "jpg", grayFile);  	
	}
	
	private static int processCharacters(char aChar) throws IOException {
		StringBuilder characters = new StringBuilder();
		char ch;		
		while ( ( ch = (char) reader.read() ) != aChar ) {
        	if ( ch == START_OF_COMMENT ) {
        		while ( reader.read() != END_OF_LINE );
        		continue;
        	}
        	characters.append(ch);
        }
		return Integer.valueOf(characters.toString());
	}
	
	private static BufferedInputStream reader;
	
	private static final char START_OF_COMMENT = '#';
	private static final char SPACE_CHARACTER = ' ';
	private static final char END_OF_LINE = '\n';
   
}	
    
final class BasicBitmapStorage {

    public BasicBitmapStorage(int aWidth, int aHeight) {
        image = new BufferedImage(aWidth, aHeight, BufferedImage.TYPE_INT_RGB);
    }

    public void fill(Color aColor) {
        Graphics graphics = image.getGraphics();
        graphics.setColor(aColor);
        graphics.fillRect(0, 0, image.getWidth(), image.getHeight());
    }    

    public Color getPixel(int aX, int aY) {
        return new Color(image.getRGB(aX, aY));
    }
    
    public void setPixel(int aX, int aY, Color aColor) {
        image.setRGB(aX, aY, aColor.getRGB());
    }
    
    public Image getImage() {
    	return image;
    }
    
    public void convertToGrayscale() {        
        for ( int y = 0; y < image.getHeight(); y++ ) {
           	for ( int x = 0; x < image.getWidth(); x++ ) {
                int color = image.getRGB(x, y);

                int alpha = ( color >> 24 ) & 255;
                int red = ( color >> 16 ) & 255;
                int green = ( color >> 8 ) & 255;
                int blue = color & 255;

                final int luminance = (int) ( 0.2126 * red + 0.7152 * green + 0.0722 * blue );

                alpha = alpha << 24;
                red = luminance << 16;
                green = luminance << 8;
                blue = luminance;

                color = alpha + red + green + blue;

                image.setRGB(x, y, color);
            }
        }
    }
    
    private final BufferedImage image;

}
Output:

Media:ColouredJava.png & Media:GrayscaleJava.png

Julia

Works with: Julia version 0.6
using Images, FileIO, Netpbm

rgbimg = load("data/bitmapInputTest.ppm")
greyimg = Gray.(rgbimg)
save("data/bitmapOutputTest.ppm", greyimg)

Kotlin

For convenience, we repeat the code for the class used in the Bitmap task here and integrate the code in the Grayscale image task within it.

// Version 1.2.40

import java.awt.Color
import java.awt.Graphics
import java.awt.image.BufferedImage
import java.io.FileInputStream
import java.io.PushbackInputStream
import java.io.File
import javax.imageio.ImageIO

class BasicBitmapStorage(width: Int, height: Int) {
    val image = BufferedImage(width, height, BufferedImage.TYPE_3BYTE_BGR)

    fun fill(c: Color) {
        val g = image.graphics
        g.color = c
        g.fillRect(0, 0, image.width, image.height)
    }

    fun setPixel(x: Int, y: Int, c: Color) = image.setRGB(x, y, c.getRGB())

    fun getPixel(x: Int, y: Int) = Color(image.getRGB(x, y))

    fun toGrayScale() {
        for (x in 0 until image.width) {
            for (y in 0 until image.height) {
                var rgb  = image.getRGB(x, y)
                val red   = (rgb shr 16) and 0xFF
                val green = (rgb shr  8) and 0xFF
                val blue  =  rgb and 0xFF
                val lumin = (0.2126 * red + 0.7152 * green + 0.0722 * blue).toInt()
                rgb = (lumin shl 16) or (lumin shl 8) or lumin
                image.setRGB(x, y, rgb)
            }
        }
    }
}

fun PushbackInputStream.skipComment() {
    while (read().toChar() != '\n') {}
}

fun PushbackInputStream.skipComment(buffer: ByteArray) {
    var nl: Int
    while (true) {
        nl = buffer.indexOf(10) // look for newline at end of comment
        if (nl != -1) break
        read(buffer)  // read another buffer full if newline not yet found
    }
    val len = buffer.size
    if (nl < len - 1) unread(buffer, nl + 1, len - nl - 1)
}

fun Byte.toUInt() = if (this < 0) 256 + this else this.toInt()

fun main(args: Array<String>) {
    // use file, output.ppm, created in the Bitmap/Write a PPM file task
    val pbis = PushbackInputStream(FileInputStream("output.ppm"), 80)
    pbis.use {
        with (it) {
            val h1 = read().toChar()
            val h2 = read().toChar()
            val h3 = read().toChar()
            if (h1 != 'P' || h2 != '6' || h3 != '\n') {
                println("Not a P6 PPM file")
                System.exit(1)
            }
            val sb = StringBuilder()
            while (true) {
                val r = read().toChar()
                if (r == '#') { skipComment(); continue }
                if (r == ' ') break  // read until space reached
                sb.append(r.toChar())
            }
            val width = sb.toString().toInt()
            sb.setLength(0)
            while (true) {
                val r = read().toChar()
                if (r == '#') { skipComment(); continue }
                if (r == '\n') break  // read until new line reached
                sb.append(r.toChar())
            }
            val height = sb.toString().toInt()
            sb.setLength(0)
            while (true) {
                val r = read().toChar()
                if (r == '#') { skipComment(); continue }
                if (r == '\n') break  // read until new line reached
                sb.append(r.toChar())
            }
            val maxCol = sb.toString().toInt()
            if (maxCol !in 0..255) {
                println("Maximum color value is outside the range 0..255")
                System.exit(1)
            }
            var buffer = ByteArray(80)
            // get rid of any more opening comments before reading data
            while (true) {
                read(buffer)
                if (buffer[0].toChar() == '#') {
                    skipComment(buffer)
                }
                else {
                    unread(buffer)
                    break
                }
            }
            // read data
            val bbs = BasicBitmapStorage(width, height)
            buffer = ByteArray(width * 3)
            var y = 0
            while (y < height) {
                read(buffer)
                for (x in 0 until width) {
                    val c = Color(
                        buffer[x * 3].toUInt(),
                        buffer[x * 3 + 1].toUInt(),
                        buffer[x * 3 + 2].toUInt()
                    )
                    bbs.setPixel(x, y, c)
                }
                y++
            }
            // convert to grayscale and save to a file
            bbs.toGrayScale()
            val grayFile = File("output_gray.jpg")
            ImageIO.write(bbs.image, "jpg", grayFile)
        }
    }
}

Lua

function Read_PPM( filename )
    local fp = io.open( filename, "rb" )    
    if fp == nil then return nil end

    local data = fp:read( "*line" )
    if data ~= "P6" then return nil end
 
    repeat
        data = fp:read( "*line" )
    until string.find( data, "#" ) == nil

    local image = {}
    local size_x, size_y
    
    size_x = string.match( data, "%d+" )
    size_y = string.match( data, "%s%d+" )

    data = fp:read( "*line" )
    if tonumber(data) ~= 255 then return nil end

    for i = 1, size_x do
        image[i] = {}
    end
 
    for j = 1, size_y do
        for i = 1, size_x do
            image[i][j] = { string.byte( fp:read(1) ), string.byte( fp:read(1) ), string.byte( fp:read(1) ) }
        end
    end
 
    fp:close()
 
    return image
end

M2000 Interpreter

Now function Bitmap has double signature. With two numbers make a bitmap,with all pixels white. With one number, expect that it is a file number and read file, and then return the bitmap.

Module Checkit {
      Function Bitmap  {
            If match("NN") then {
                 Read x as long, y as long
            } else.if Match("N") Then  {
                \\ is a file?
                  Read f
                  if not Eof(f) then {
                        Line Input #f,  p3$
                              If p3$="P3" Then {
                                    Line Input #f, Comment$
                                    if left$(Comment$,1)="#" then {
                                          Line Input #f, Dimension$
                                    } else  Dimension$=Comment$
                                    long x=Val(piece$(Dimension$," ")(0))
                                    long y=Val(piece$(Dimension$," ")(1))
                                    do {
                                          Line Input #f, P255$
                                    } until left$(P255$, 1)<>"#"
                                    If not P255$="255" then Error "Not proper ppm format"
                              }                  
                  }
            } else Error "No proper arguments"
            
            
            if x<1 or y<1 then  Error "Wrong dimensions"
            structure rgb {
                  red as byte
                  green as byte
                  blue as byte
            }
            m=len(rgb)*x mod 4
            if m>0 then m=4-m  ' add some bytes to raster line
            m+=len(rgb) *x
            Structure rasterline {
                  { 
                        pad as byte*m
                  }   
                  \\ union pad+hline
                  hline as rgb*x
            }
      
            Structure Raster {
                  magic as integer*4
                  w as integer*4
                  h as integer*4
                  lines as rasterline*y
            }
            Buffer Clear Image1 as Raster
            \\ 24 chars as header to be used from bitmap render build in functions
            Return Image1, 0!magic:="cDIB", 0!w:=Hex$(x,2), 0!h:=Hex$(y, 2)
            \\ fill white (all 255)
            \\ Str$(string) convert to ascii, so we get all characters from words  width to byte width
            if not valid(f) then  Return Image1, 0!lines:=Str$(String$(chrcode$(255), Len(rasterline)*y))
            Buffer Clear Pad as Byte*4
            SetPixel=Lambda Image1, Pad,aLines=Len(Raster)-Len(Rasterline), blines=-Len(Rasterline) (x, y, c) ->{
                  where=alines+3*x+blines*y
                  if c>0 then c=color(c)
                  c-!
                  Return Pad, 0:=c as long
                  Return Image1, 0!where:=Eval(Pad, 2) as byte, 0!where+1:=Eval(Pad, 1) as byte, 0!where+2:=Eval(Pad, 0) as byte
            
            }
            GetPixel=Lambda Image1,aLines=Len(Raster)-Len(Rasterline), blines=-Len(Rasterline) (x,y) ->{
                  where=alines+3*x+blines*y
                  =color(Eval(image1, where+2 as byte), Eval(image1, where+1 as byte), Eval(image1, where as byte))
            }
            StrDib$=Lambda$ Image1, Raster -> {
                  =Eval$(Image1, 0, Len(Raster))
            }
            CopyImage=Lambda Image1 (image$) -> {
                  if left$(image$,12)=Eval$(Image1, 0, 24 ) Then  {
                         Return Image1, 0:=Image$
                  } Else Error "Can't Copy Image"
            }
            Export2File=Lambda Image1, x, y (f) -> {
                  \\ use this between open and close 
                  Print #f, "P3"
                  Print #f,"# Created using M2000 Interpreter"
                  Print #f, x;" ";y
                  Print #f, 255
                  x2=x-1
                  where=24
                  For y1= 0 to y-1 {
                        a$=""
                        For x1=0 to x2 {
                              Print #f, a$;Eval(Image1, where+2 as byte);" ";
                              Print #f,  Eval(Image1, where+1 as byte);" ";
                              Print #f,  Eval(Image1, where as byte);
                              where+=3
                              a$=" "
                        }
                        Print #f
                        m=where mod 4
                        if m<>0 then where+=4-m
                  }            
            }
            if valid(F) then {
                  'load  RGB values form file
                  x0=x-1
                  where=24
                        For y1=y-1 to 0 {
                              do {
                                          Line Input #f, aline$
                              } until left$(aline$,1)<>"#"
                              flush   ' empty stack
                              Stack aline$  ' place all values to stack as FIFO         
                              For x1=0 to x0 {
                                    \\ now read from stack using Number
                                    Return Image1, 0!where+2:=Number as byte, 0!where+1:=Number as byte, 0!where:=Number as byte
                                    where+=3
                              }
                              m=where mod 4
                              if m<>0 then where+=4-m                                   
                        }
            }
            Group Bitmap {
                  SetPixel=SetPixel
                  GetPixel=GetPixel
                  Image$=StrDib$
                  Copy=CopyImage
                  ToFile=Export2File
            }
            =Bitmap
      }
      A=Bitmap(10, 10)
      Call A.SetPixel(5,5, color(128,0,255))
      Open "A.PPM" for Output as #F
            Call A.ToFile(F)
      Close #f
      Open "A.PPM" for Input as #F
      Try {
            C=Bitmap(f)     
            Copy 400*twipsx,200*twipsy use C.Image$()
      }
      Close #f
      ' is the same as this one
        Open "A.PPM" for Input as #F
            Line Input #f,  p3$
            If p3$="P3" Then {
                  Line Input #f, Comment$
                  if left$(Comment$,1)="#" then {
                        Line Input #f, Dimension$
                  } else  Dimension$=Comment$
                  Long x=Val(piece$(Dimension$," ")(0))
                  Long y=Val(piece$(Dimension$," ")(1))
                  do {
                        Line Input #f, P255$
                  } until left$(P255$, 1)<>"#"
                  If not P255$="255" then Error "Not proper ppm format"
                  B=Bitmap(x, y)
                  x0=x-1
                  For y1=y-1 to 0 {
                        do {
                                    Line Input #f, aline$
                        } until left$(aline$,1)<>"#"
                        flush   ' empty stack
                        Stack aline$  ' place all values to stack as FIFO         
                        For x1=0 to x0 {
                              \\ now read from stack
                              Read red, green, blue
                              Call B.setpixel(x1, y1, Color(red, green, blue))
                        }
                  }
            }
      Close #f
      If valid("B") then  Copy 200*twipsx,200*twipsy use B.Image$()
}
Checkit

Mathematica / Wolfram Language

Import["file.ppm","PPM"]

Nim

import strutils
import bitmap
import streams

type FormatError = object of CatchableError

# States used to parse the header.
type State = enum waitingMagic, waitingWidth, waitingHeight, waitingColors

#---------------------------------------------------------------------------------------------------

iterator tokens(f: Stream): tuple[value: string, lastInLine: bool] =
  ## Yield the tokens in the header.
  for line in f.lines:
    if not line.startsWith('#'):
      let fields = line.splitWhitespace()
      for i, t in fields:
        yield (t, i == fields.high)

#---------------------------------------------------------------------------------------------------

proc getInt(s: string): int {.inline.} =
  ## Try to parse an int. Raise an exception if not an integer.
  try:
    result = s.parseInt()
  except ValueError:
    raise newException(FormatError, "Invalid value")

#---------------------------------------------------------------------------------------------------

proc header(f: Stream): tuple[width, height: Index] =
  ## Read the header and retrun the image width and height.
  var state = waitingMagic
  for (token, lastInLine) in f.tokens:
    case state
    of waitingMagic:
      if token != "P6":
        raise newException(FormatError, "Invalid file header")
    of waitingWidth:
      result.width = token.getInt()
    of waitingHeight:
      result.height = token.getInt()
    of waitingColors:
      if token.getInt() != 255:
        raise newException(FormatError, "Invalid number of colors")
      if not lastInLine:
        raise newException(FormatError, "Invalid data after number of colors")
      break
    state = succ(state)

#---------------------------------------------------------------------------------------------------

proc readPPM*(f: Stream): Image =
  ## Read a PPM file from a stream into an image.

  let header = f.header()
  result = newImage(header.width, header.height)

  var
    arr: array[256, int8]
    read = f.readData(addr(arr), 256)
    pos = 0

  while read != 0:
    for i in 0 ..< read:
      case pos mod 3
      of 0: result.pixels[pos div 3].r = arr[i].uint8
      of 1: result.pixels[pos div 3].g = arr[i].uint8
      of 2: result.pixels[pos div 3].b = arr[i].uint8
      else: discard
      inc pos

    read = f.readData(addr(arr), 256)

  if pos != 3 * result.w * result.h:
    raise newException(FormatError, "Truncated file")

#---------------------------------------------------------------------------------------------------

proc readPPM*(filename: string): Image =
  ## Load a PPM file into an image.

  var file = openFileStream(filename, fmRead)
  result = file.readPPM()
  file.close()

#———————————————————————————————————————————————————————————————————————————————————————————————————

when isMainModule:
  let image = readPPM("output.ppm")
  echo image.h, " ", image.w

OCaml

let read_ppm ~filename =
  let ic = open_in filename in
  let line = input_line ic in
  if line <> "P6" then invalid_arg "not a P6 ppm file";
  let line = input_line ic in
  let line =
    try if line.[0] = '#'  (* skip comments *)
    then input_line ic
    else line
    with _ -> line
  in
  let width, height =
    Scanf.sscanf line "%d %d" (fun w h -> (w, h))
  in
  let line = input_line ic in
  if line <> "255" then invalid_arg "not a 8 bit depth image";
  let all_channels =
    let kind = Bigarray.int8_unsigned
    and layout = Bigarray.c_layout
    in
    Bigarray.Array3.create kind layout 3 width height
  in
  let r_channel = Bigarray.Array3.slice_left_2 all_channels 0
  and g_channel = Bigarray.Array3.slice_left_2 all_channels 1
  and b_channel = Bigarray.Array3.slice_left_2 all_channels 2
  in
  for y = 0 to pred height do
    for x = 0 to pred width do
      r_channel.{x,y} <- (input_byte ic);
      g_channel.{x,y} <- (input_byte ic);
      b_channel.{x,y} <- (input_byte ic);
    done;
  done;
  close_in ic;
  (all_channels,
   r_channel,
   g_channel,
   b_channel)

and converting a given color file to grayscale:

let () =
  let img = read_ppm ~filename:"logo.ppm" in
  let img = to_color(to_grayscale ~img) in
  output_ppm ~oc:stdout ~img;
;;

sending the result to stdout allows to see the result without creating a temporary file sending it through a pipe to the display utility of ImageMagick:

ocaml script.ml | display -

Oz

The read function in module "BitmapIO.oz":

functor
import
   Bitmap
   Open
export
   Read
   %% Write
define
   fun {Read Filename}
      F = {New Open.file init(name:Filename)}

      fun {ReadColor8 _}
	 Bytes = {F read(list:$ size:3)}
      in
	 {List.toTuple color Bytes}
      end

      fun {ReadColor16 _}
	 Bytes = {F read(list:$ size:6)}
      in
	 {List.toTuple color {Map {PairUp Bytes} FromBytes}}
      end
   in
      try
	 Magic = {F read(size:2 list:$)}
	 if Magic \= "P6" then raise bitmapIO(read unsupportedFormat(Magic)) end end
	 Width = {ReadNumber F}
	 Height = {ReadNumber F}
	 MaxVal = {ReadNumber F}
	 MaxVal =< 0xffff = true
	 Reader = if MaxVal =< 0xff then ReadColor8 else ReadColor16 end
	 B = {Bitmap.new Width Height}
      in
	 {Bitmap.transform B Reader}
	 B
      finally
	 {F close}
      end
   end

   fun {ReadNumber F}
      Ds
   in
      {SkipWS F}
      Ds = for collect:Collect break:Break do
	      [C] = {F read(list:$ size:1)}
	   in
	      if {Char.isDigit C} then {Collect C}
	      else {Break}
	      end
	   end
      {SkipWS F}
      {String.toInt Ds}
   end

   proc {SkipWS F}
      [C] = {F read(list:$ size:1)}
   in
      if {Char.isSpace C} then {SkipWS F}
      elseif C == &# then
	 {SkipLine F}
      else
	 {F seek(whence:current offset:~1)}
      end
   end

   proc {SkipLine F}
      [C] = {F read(list:$ size:1)}
   in
      if C \= &\n andthen  C \= &\r then {SkipLine F} end
   end
   
   fun {PairUp Xs}
      case Xs of X1|X2|Xr then [X1 X2]|{PairUp Xr}
      [] nil then nil
      end
   end

   fun {FromBytes [C1 C2]}
      C1 * 0x100 + C2
   end

   %% Omitted: Write
end

The actual task:

declare
  [BitmapIO Grayscale] = {Module.link ['BitmapIO.ozf' 'Grayscale.ozf']}

  B = {BitmapIO.read "image.ppm"}
  G = {Grayscale.toGraymap B}
in
  {BitmapIO.write {Grayscale.fromGraymap G} "greyimage.ppm"}

Perl

Library: Imlib2
#! /usr/bin/perl

use strict;
use Image::Imlib2;

my $img = Image::Imlib2->load("out0.ppm");

# let's do something with it now
$img->set_color(255, 255, 255, 255);
$img->draw_line(0,0, $img->width,$img->height);
$img->image_set_format("png");
$img->save("out1.png");

exit 0;

Phix

Based on Euphoria, requires write_ppm() from Write_a_PPM_file, to_grey from Grayscale_image
Note that demo\rosetta\Bitmap_read_ppm.exw is just the last 3 lines with the include ppm.e since that contains the read_ppm() (abeit with a few more options and other tweaks) also used by several other examples, and covers the above requirements. Results may be verified with demo\rosetta\viewppm.exw

-- demo\rosetta\Bitmap_read_ppm.exw (runnable version)

function read_ppm(string filename)
sequence image, line
integer dimx, dimy, maxcolor
atom fn = open(filename, "rb")
    if fn<0 then
        return -1 -- unable to open
    end if
    line = gets(fn)
    if line!="P6\n" then
        return -1 -- only ppm6 files are supported
    end if
    line = gets(fn)
    {{dimx,dimy}} = scanf(line,"%d %d%s")
    line = gets(fn)
    {{maxcolor}} = scanf(line,"%d%s")
    image = repeat(repeat(0,dimy),dimx)
    for y=1 to dimy do
        for x=1 to dimx do
            image[x][y] = getc(fn)*#10000 + getc(fn)*#100 + getc(fn)
        end for
    end for
    close(fn)
    return image
end function

--include ppm.e   -- read_ppm(), write_ppm(), to_grey()  (as distributed, instead of the above)
 
sequence img = read_ppm("Lena.ppm")
img = to_grey(img)
write_ppm("LenaGray.ppm",img)

PicoLisp

(de ppmRead (File)
   (in File
      (unless (and `(hex "5036") (rd 2))  # P6
         (quit "Wrong file format" File) )
      (rd 1)
      (let (DX 0  DY 0  Max 0  C)
         (while (>= 9 (setq C (- (rd 1) `(char "0"))) 0)
            (setq DX (+ (* 10 DX) C)) )
         (while (>= 9 (setq C (- (rd 1) `(char "0"))) 0)
            (setq DY (+ (* 10 DY) C)) )
         (while (>= 9 (setq C (- (rd 1) `(char "0"))) 0)
            (setq Max (+ (* 10 Max) C)) )
         (prog1
            (make (do DY (link (need DX))))
            (for Y @
               (map
                  '((X) (set X (list (rd 1) (rd 1) (rd 1))))
                  Y ) ) ) ) ) )

Read a color image "img.ppm", convert and write to "img.pgm":

(pgmWrite (ppm->pgm (ppmRead "img.ppm")) "img.pgm")

PL/I

/* BITMAP FILE: read in a file in PPM format, P6 (binary). 14/5/2010 */
test: procedure options (main);
   declare (m, n, max_color, i, j) fixed binary (31);
   declare ch character (1), ID character (2);
   declare 1 pixel union,
            2 color bit(24) aligned,
            2 primary_colors,
               3 R char (1),
               3 G char (1),
               3 B char (1);
   declare in file record;

   open file (in) title ('/IMAGE.PPM,TYPE(FIXED),RECSIZE(1)' ) input;

   call get_char;
   ID = ch;
   call get_char;
   substr(ID, 2,1) = ch;
   /* Read in the dimensions of the image */
   call get_integer (m);
   call get_integer (n);

   /* Read in the maximum color size used */
   call get_integer (max_color);
      /* The previous call reads in ONE line feed or CR or other terminator */
      /* character. */

begin;
   declare image (0:m-1,0:n-1) bit (24);

   do i = 0 to hbound(image, 1);
      do j = 0 to hbound(image,2);
         read file (in) into (R);
         read file (in) into (G);
         read file (in) into (B);
         image(i,j) = color;
      end;
   end;
end;

get_char: procedure;
   do until (ch ^= ' ');
      read file (in) into (ch);
   end;
end get_char;

get_integer: procedure (value);
   declare value fixed binary (31);

   do until (ch = ' ');
      read file (in) into (ch);
   end;
   value = 0;
   do until (is_digit(ch));
      value = value*10 + ch;
      read file (in) into (ch);
   end;
end get_integer;

is_digit: procedure (ch) returns (bit(1));
   declare ch character (1);
   return (index('0123456789', ch) > 0);
end is_digit;
end test;

PureBasic

Structure PPMColor
  r.c
  g.c
  b.c
EndStructure

Procedure LoadImagePPM(Image, file$)
  ; Author Roger Rösch (Nickname Macros)
  IDFile = ReadFile(#PB_Any, file$)
  If IDFile
    If CreateImage(Image, 1, 1)
      Format$ = ReadString(IDFile)
      ReadString(IDFile) ; skip comment
      Dimensions$ = ReadString(IDFile)
      w           = Val(StringField(Dimensions$, 1, " "))
      h           = Val(StringField(Dimensions$, 2, " "))
      ResizeImage(Image, w, h)
      StartDrawing(ImageOutput(Image))
      max = Val(ReadString(IDFile))           ; Maximal Value for a color
      Select Format$
        Case "P3" ; File in ASCII format
          ; Exract everey number remaining in th file into an array using an RegEx
          Stringlen = Lof(IDFile) - Loc(IDFile)
          content$  = Space(Stringlen)
          Dim color.s(0)
          ReadData(IDFile, @content$, Stringlen)
          CreateRegularExpression(1, "\d+")
          ExtractRegularExpression(1, content$, color())
          ; Plot color information on our empty Image
          For y = 0 To h - 1
            For x = 0 To w - 1
              pos = (y*w + x)*3
              r=Val(color(pos))*255 / max
              g=Val(color(pos+1))*255 / max
              b=Val(color(pos+2))*255 / max
              Plot(x, y, RGB(r,g,b))
            Next
          Next
        Case "P6" ;File In binary format
          ; Read whole bytes into a buffer because its faster than reading single ones
          Bufferlen = Lof(IDFile) - Loc(IDFile)
          *Buffer   = AllocateMemory(Bufferlen)
          ReadData(IDFile, *Buffer, Bufferlen)
          ; Plot color information on our empty Image
          For y = 0 To h - 1
            For x = 0 To w - 1
              *color.PPMColor = pos + *Buffer
              Plot(x, y, RGB(*color\r*255 / max, *color\g*255 / max, *color\b*255 / max))
              pos + 3
            Next
          Next
      EndSelect
      StopDrawing()
      ; Return 1 if successfully loaded to behave as other PureBasic functions
      ProcedureReturn 1 
    EndIf
  EndIf
EndProcedure

To complete the task, the following code should be added to the above fragment and to the PureBasic solutions for Grayscale image and Write a PPM file

Define file.s, file2.s, image = 3
file = OpenFileRequester("Select source image file", "", "PPM image (*.ppm)|*.ppm", 0)
If file And LCase(GetExtensionPart(file)) = "ppm"
  LoadImagePPM(image, file)
  ImageGrayout(image)
  file2 = Left(file, Len(file) - Len(GetExtensionPart(file))) + "_grayscale." + GetExtensionPart(file)
  SaveImageAsPPM(image, file2, 1)
EndIf

Python

Works with: Python version 3.1

Extending the example given here

# With help from http://netpbm.sourceforge.net/doc/ppm.html

# String masquerading as ppm file (version P3)
import io

ppmtxt = '''P3
# feep.ppm
4 4
15
 0  0  0    0  0  0    0  0  0   15  0 15
 0  0  0    0 15  7    0  0  0    0  0  0
 0  0  0    0  0  0    0 15  7    0  0  0
15  0 15    0  0  0    0  0  0    0  0  0
'''


def tokenize(f):
    for line in f:
        if line[0] != '#':
            for t in line.split():
                yield t

def ppmp3tobitmap(f):
    t = tokenize(f)
    nexttoken = lambda : next(t)
    assert 'P3' == nexttoken(), 'Wrong filetype'
    width, height, maxval = (int(nexttoken()) for i in range(3))
    bitmap = Bitmap(width, height, Colour(0, 0, 0))
    for h in range(height-1, -1, -1):
        for w in range(0, width):
            bitmap.set(w, h, Colour( *(int(nexttoken()) for i in range(3))))

    return bitmap
    
print('Original Colour PPM file')
print(ppmtxt)
ppmfile = io.StringIO(ppmtxt)
bitmap = ppmp3tobitmap(ppmfile)
print('Grey PPM:')
bitmap.togreyscale()
ppmfileout = io.StringIO('')
bitmap.writeppmp3(ppmfileout)
print(ppmfileout.getvalue())


'''
The print statements above produce the following output:

Original Colour PPM file
P3
# feep.ppm
4 4
15
 0  0  0    0  0  0    0  0  0   15  0 15
 0  0  0    0 15  7    0  0  0    0  0  0
 0  0  0    0  0  0    0 15  7    0  0  0
15  0 15    0  0  0    0  0  0    0  0  0

Grey PPM:
P3
# generated from Bitmap.writeppmp3
4 4
11
    0  0  0    0  0  0    0  0  0    4  4  4
    0  0  0   11 11 11    0  0  0    0  0  0
    0  0  0    0  0  0   11 11 11    0  0  0
    4  4  4    0  0  0    0  0  0    0  0  0

'''

Racket

#lang racket
(require racket/draw)

(define (read-ppm port)
  (parameterize ([current-input-port port])
    (define magic (read))
    (define width (read))
    (define height (read))
    (define maxcol (read))
    (define bm (make-object bitmap% width height))
    (define dc (new bitmap-dc% [bitmap bm]))
    (send dc set-smoothing 'unsmoothed)
    (define (adjust v) (* 255 (/ v maxcol)))
    (for/list ([x width])
      (for/list ([y height])
        (define red (read))
        (define green (read))
        (define blue (read))
        (define color (make-object color% (adjust red) (adjust green) (adjust blue)))
        (send dc set-pen color 1 'solid)
        (send dc draw-point x y)))
    bm))

Raku

(formerly Perl 6)

Works with: Rakudo version 2017.09

Uses pieces from Bitmap, Write a PPM file and Grayscale image tasks. Included here to make a complete, runnable program.

class Pixel { has UInt ($.R, $.G, $.B) }
class Bitmap {
    has UInt ($.width, $.height);
    has Pixel @.data;
}

role PGM {
    has @.GS;
    method P5 returns Blob {
	"P5\n{self.width} {self.height}\n255\n".encode('ascii')
	~ Blob.new: self.GS
    }
}

sub load-ppm ( $ppm ) {
    my $fh    = $ppm.IO.open( :enc('ISO-8859-1') );
    my $type  = $fh.get;
    my ($width, $height) = $fh.get.split: ' ';
    my $depth = $fh.get;
    Bitmap.new( width => $width.Int, height => $height.Int,
      data => ( $fh.slurp.ords.rotor(3).map:
        { Pixel.new(R => $_[0], G => $_[1], B => $_[2]) } )
    )
}

sub grayscale ( Bitmap $bmp ) {
    $bmp.GS = map { (.R*0.2126 + .G*0.7152 + .B*0.0722).round(1) min 255 }, $bmp.data;
}

my $filename = './camelia.ppm';

my Bitmap $b = load-ppm( $filename ) but PGM;

grayscale($b);

'./camelia-gs.pgm'.IO.open(:bin, :w).write: $b.P5;

See camelia, and camelia-gs images. (converted to .png as .ppm format is not widely supported).

REXX

The input file   Lenna50.ppm   is a PPM format of
the input file    Lenna50.jpg    used elsewhere on Rosetta Code.

This REXX program handles alternative delimiters as well as comments within the PPM header.

/*REXX program reads a PPM formatted image file,  and creates a gray─scale image of it. */
parse arg iFN oFN                                /*obtain optional argument from the CL.*/
if iFN=='' | iFN==","  then  iFN= 'Lenna50'      /*Not specified?  Then use the default.*/
if oFN=='' | oFN==","  then  oFN= 'greyscale'    /* "      "         "   "   "     "    */
iFID= iFN'.ppm';             oFID= oFN'.ppm'     /*complete the  input and output  FIDs.*/
call charin iFID, 1, 0                           /*set the position of the input file.  */
y=charin(iFID, , copies(9, digits() ) )          /*read the entire input file  ───►  X  */
parse var  y   id  3 c 4 3 width height # pixels /*extract header info from the PPM hdr.*/
      LF= 'a'x                                   /*define a comment separator  (in hdr).*/      /* ◄─── LF delimiters & comments*/
if c==LF  then do;  commentEND=pos(LF, y, 4)     /*point to the last char in the comment*/      /* ◄─── LF delimiters & comments*/
                    parse var  y   =(commentEND)  +1  width  height          #  pixels          /* ◄─── LF delimiters & comments*/
               end                                                                              /* ◄─── LF delimiters & comments*/
                                                 /* [↓]  has an alternative delimiter?  */      /* ◄─── LF delimiters & comments*/
z=pos(LF, height);  if z\==0  then parse var  height height    =(z)   +1     #  pixels          /* ◄─── LF delimiters & comments*/
z=pos(LF, #     );  if z\==0  then parse var  #      #         =(z)   +1        pixels          /* ◄─── LF delimiters & comments*/
chunk=4000                                       /*chunk size to be written at one time.*/
LenPixels= length(pixels)

  do j=0  for 256;  _=d2c(j);   @._=j;   @@.j=_  /*build two tables for fast conversions*/
  end   /*j*/

call charout oFID, ,  1                          /*set the position of the output file. */
call charout oFID, id || width height #' '       /*write the header followed by a blank.*/
!=1
    do until !>=LenPixels;            $=         /*$:      partial output string so far.*/
      do !=!  by 3  for chunk                    /*chunk:  # pixels converted at 1 time.*/
      parse var pixels  =(!)  r +1   g +1   b +1 /*obtain the next  RGB  of a PPM pixel.*/
      if r==''  then leave                       /*has the end─of─string been reached?  */
      _=(.2126*@.r  + .7152*@.g  + .0722*@.b )%1 /*an integer RGB greyscale of a pixel. */
      $=$  ||  @@._  ||  @@._  ||  @@._          /*lump (grey)  R G B  pixels together. */
      end   /*!*/                                /* [↑]  D2C  converts decimal ───► char*/
    call charout oFID, $                         /*write the next bunch of pixels.      */
    end     /*until*/

call charout oFID                                /*close the output file just to be safe*/
say 'File '       oFID       " was created."     /*stick a fork in it,  we're all done. */
output:
File  greyscale.ppm  was created.

Ruby

Extending Basic_bitmap_storage#Ruby

class Pixmap
  # 'open' is a class method
  def self.open(filename)
    bitmap = nil
    File.open(filename, 'r') do |f|
      header = [f.gets.chomp, f.gets.chomp, f.gets.chomp]
      width, height = header[1].split.map {|n| n.to_i }
      if header[0] != 'P6' or header[2] != '255' or width < 1 or height < 1
        raise StandardError, "file '#{filename}' does not start with the expected header"
      end
      f.binmode
      bitmap = self.new(width, height)
      height.times do |y|
        width.times do |x|
          # read 3 bytes
          red, green, blue = f.read(3).unpack('C3')
          bitmap[x,y] = RGBColour.new(red, green, blue)
        end
      end
    end
    bitmap
  end
end

# create an image: a green cross on a blue background
colour_bitmap = Pixmap.new(20, 30)
colour_bitmap.fill(RGBColour::BLUE)
colour_bitmap.height.times {|y| [9,10,11].each {|x| colour_bitmap[x,y]=RGBColour::GREEN}}
colour_bitmap.width.times  {|x| [14,15,16].each {|y| colour_bitmap[x,y]=RGBColour::GREEN}}
colour_bitmap.save('testcross.ppm')

# then, convert to grayscale
Pixmap.open('testcross.ppm').to_grayscale!.save('testgray.ppm')

Rust

parser.rs:
use super::{Color, ImageFormat};
use std::str::from_utf8;
use std::str::FromStr;

pub fn parse_version(input: &[u8]) -> nom::IResult<&[u8], ImageFormat> {
    use nom::branch::alt;
    use nom::bytes::complete::tag;
    use nom::character::complete::line_ending;
    use nom::combinator::map;
    use nom::sequence::terminated;

    // starts with P3/P6 ends with a CR/LF
    terminated(
        alt((
            map(tag("P3".as_bytes()), |_| ImageFormat::P3),
            map(tag("P6".as_bytes()), |_| ImageFormat::P6),
        )),
        line_ending,
    )(input)
}

pub fn parse_image_attributes(input: &[u8]) -> nom::IResult<&[u8], (usize, usize, usize)> {
    use nom::character::complete::line_ending;
    use nom::character::complete::{digit1, space1};
    use nom::sequence::terminated;
    use nom::sequence::tuple;

    // 3 numbers separated by spaces ends with a CR/LF
    terminated(tuple((digit1, space1, digit1, space1, digit1)), line_ending)(input).map(
        |(next_input, result)| {
            (
                next_input,
                (
                    usize::from_str_radix(from_utf8(result.0).unwrap(), 10).unwrap(),
                    usize::from_str_radix(from_utf8(result.2).unwrap(), 10).unwrap(),
                    usize::from_str_radix(from_utf8(result.4).unwrap(), 10).unwrap(),
                ),
            )
        },
    )
}

pub fn parse_color_binary(input: &[u8]) -> nom::IResult<&[u8], Color> {
    use nom::number::complete::u8 as nom_u8;
    use nom::sequence::tuple;

    tuple((nom_u8, nom_u8, nom_u8))(input).map(|(next_input, res)| {
        (
            next_input,
            Color {
                red: res.0,
                green: res.1,
                blue: res.2,
            },
        )
    })
}

pub fn parse_data_binary(input: &[u8]) -> nom::IResult<&[u8], Vec<Color>> {
    use nom::multi::many0;
    many0(parse_color_binary)(input)
}

pub fn parse_color_ascii(input: &[u8]) -> nom::IResult<&[u8], Color> {
    use nom::character::complete::{digit1, space0, space1};
    use nom::sequence::tuple;

    tuple((digit1, space1, digit1, space1, digit1, space0))(input).map(|(next_input, res)| {
        (
            next_input,
            Color {
                red: u8::from_str(from_utf8(res.0).unwrap()).unwrap(),
                green: u8::from_str(from_utf8(res.2).unwrap()).unwrap(),
                blue: u8::from_str(from_utf8(res.4).unwrap()).unwrap(),
            },
        )
    })
}

pub fn parse_data_ascii(input: &[u8]) -> nom::IResult<&[u8], Vec<Color>> {
    use nom::multi::many0;
    many0(parse_color_ascii)(input)
}


lib.rs:
extern crate nom;
extern crate thiserror;
mod parser;

use std::default::Default;
use std::fmt;
use std::io::{BufWriter, Error, Write};
use std::ops::{Index, IndexMut};
use std::{fs::File, io::Read};
use thiserror::Error;

#[derive(Copy, Clone, Default, PartialEq, Debug)]
pub struct Color {
    pub red: u8,
    pub green: u8,
    pub blue: u8,
}

#[derive(Copy, Clone, PartialEq, Debug)]
pub enum ImageFormat {
    P3,
    P6,
}

impl From<&str> for ImageFormat {
    fn from(i: &str) -> Self {
        match i.to_lowercase().as_str() {
            "p3" => ImageFormat::P3,
            "p6" => ImageFormat::P6,
            _ => unimplemented!("no other formats supported"),
        }
    }
}

impl fmt::Display for ImageFormat {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            ImageFormat::P3 => {
                write!(f, "P3")
            }
            ImageFormat::P6 => {
                write!(f, "P6")
            }
        }
    }
}

#[derive(Error, Debug)]
pub enum ImageError {
    #[error("File not found")]
    FileNotFound,
    #[error("File not readable")]
    FileNotReadable,
    #[error("Invalid header information")]
    InvalidHeader,
    #[error("Invalid information in the data block")]
    InvalidData,
    #[error("Invalid max color information")]
    InvalidMaxColor,
    #[error("File is incomplete")]
    IncompleteFile,
    #[error("unknown data store error")]
    Unknown,
}
pub struct Image {
    pub format: ImageFormat,
    pub width: usize,
    pub height: usize,
    pub data: Vec<Color>,
}

impl Image {
    #[must_use]
    pub fn new(width: usize, height: usize) -> Self {
        Self {
            format: ImageFormat::P6,
            width,
            height,
            data: vec![Color::default(); width * height],
        }
    }

    pub fn fill(&mut self, color: Color) {
        for elem in &mut self.data {
            *elem = color;
        }
    }

    /// # Errors
    ///
    /// Will return `Error` if `filename` does not exist or the user does not have
    /// permission to write to it, or the write operation fails.
    pub fn write_ppm(&self, filename: &str) -> Result<(), Error> {
        let file = File::create(filename)?;
        let mut writer = BufWriter::new(file);
        writeln!(&mut writer, "{}", self.format.to_string())?;
        writeln!(&mut writer, "{} {} 255", self.width, self.height)?;
        match self.format {
            ImageFormat::P3 => {
                writer.write_all(
                    &self
                        .data
                        .iter()
                        .flat_map(|color| {
                            vec![
                                color.red.to_string(),
                                color.green.to_string(),
                                color.blue.to_string(),
                            ]
                        })
                        .collect::<Vec<String>>()
                        .join(" ")
                        .as_bytes(),
                )?;
            }
            ImageFormat::P6 => {
                writer.write_all(
                    &self
                        .data
                        .iter()
                        .flat_map(|color| vec![color.red, color.green, color.blue])
                        .collect::<Vec<u8>>(),
                )?;
            }
        }
        Ok(())
    }

    /// # Panics
    ///
    /// Panics if the format is not P6 or P3 PPM
    /// # Errors
    ///
    /// Will return `Error` if `filename` does not exist or the user does not have
    /// permission to read it or the read operation fails, or the file format does not
    /// match the specification
    pub fn read_ppm(filename: &str) -> Result<Image, ImageError> {
        let mut file = File::open(filename).map_err(|_| ImageError::FileNotFound)?;
        let mut data: Vec<u8> = Vec::new();
        file.read_to_end(&mut data)
            .map_err(|_| ImageError::FileNotReadable)?;

        let (i, format) = parser::parse_version(&data).map_err(|_| ImageError::InvalidHeader)?;
        let (i, (width, height, max_color)) =
            parser::parse_image_attributes(i).map_err(|_| ImageError::InvalidHeader)?;

        if max_color != 255 {
            return Err(ImageError::InvalidMaxColor);
        }

        let (_, data) = match format {
            ImageFormat::P3 => parser::parse_data_ascii(i).map_err(|_| ImageError::InvalidData)?,
            ImageFormat::P6 => parser::parse_data_binary(i).map_err(|_| ImageError::InvalidData)?,
        };

        if data.len() != height * width {
            return Err(ImageError::IncompleteFile);
        };

        Ok(Image {
            format,
            width,
            height,
            data,
        })
    }
}

impl Index<(usize, usize)> for Image {
    type Output = Color;

    fn index(&self, (x, y): (usize, usize)) -> &Color {
        &self.data[x + y * self.width]
    }
}

impl IndexMut<(usize, usize)> for Image {
    fn index_mut(&mut self, (x, y): (usize, usize)) -> &mut Color {
        &mut self.data[x + y * self.width]
    }
}


use bitmap::Image;

// see read_ppm implementation in the bitmap library

pub fn main() {
    // read a PPM image, which was produced by the write-a-ppm-file task
    let image = Image::read_ppm("./test_image.ppm").unwrap();

    println!("Read using nom parsing:");
    println!("Format: {:?}", image.format);
    println!("Dimensions: {} x {}", image.height, image.width);
}

Scala

Uses the Basic Bitmap Storage and Grayscale Bitmap classes.

See also Task Write a PPM File for save code.

import scala.io._
import scala.swing._
import java.io._
import java.awt.Color
import javax.swing.ImageIcon

object Pixmap {
   private case class PpmHeader(format:String, width:Int, height:Int, maxColor:Int)
	
   def load(filename:String):Option[RgbBitmap]={
      implicit val in=new BufferedInputStream(new FileInputStream(filename))
      val header=readHeader
      if(header.format=="P6")
      {
         val bm=new RgbBitmap(header.width, header.height);
         for(y <- 0 until bm.height; x <- 0 until bm.width; c=readColor)
            bm.setPixel(x, y, c)
         return Some(bm)
      }
      None
   }

   private def readHeader(implicit in:InputStream)={
      var format=readLine
		
      var line=readLine
      while(line.startsWith("#"))   //skip comments
         line=readLine

      val parts=line.split("\\s")
      val width=parts(0).toInt
      val height=parts(1).toInt
      val maxColor=readLine.toInt
		
      new PpmHeader(format, width, height, maxColor)
   }

   private def readColor(implicit in:InputStream)=new Color(in.read, in.read, in.read)

   private def readLine(implicit in:InputStream)={
      var out=""
      var b=in.read
      while(b!=0xA){out+=b.toChar; b=in.read}
      out
   }
}

Usage:

object PixmapTest {
   def main(args: Array[String]): Unit = {
      val img=Pixmap.load("image.ppm").get
      val grayImg=BitmapOps.grayscale(img);
      Pixmap.save(grayImg, "image_gray.ppm")

      val mainframe=new MainFrame(){
         title="Test"
         visible=true
         contents=new Label(){
            icon=new ImageIcon(grayImg.image)
         }
      }
   }
}

Seed7

$ include "seed7_05.s7i";
  include "draw.s7i";
  include "color.s7i";

const func PRIMITIVE_WINDOW: getPPM (in string: fileName) is func
  result
    var PRIMITIVE_WINDOW: aWindow is PRIMITIVE_WINDOW.value;
  local
    var file: ppmFile is STD_NULL;
    var string: line is "";
    var integer: width is 0;
    var integer: height is 0;
    var integer: x is 0;
    var integer: y is 0;
    var color: pixColor is black;
  begin
    ppmFile := open(fileName, "r");
    if ppmFile <> STD_NULL then
      if getln(ppmFile) = "P6" then
        repeat
          line := getln(ppmFile);
        until line = "" or line[1] <> '#';
        read(ppmFile, width);
        readln(ppmFile, height);
        aWindow := newPixmap(width, height);
        for y range 0 to pred(height) do
          for x range 0 to pred(width) do
            pixColor.redLight   := ord(getc(ppmFile));
            pixColor.greenLight := ord(getc(ppmFile));
            pixColor.blueLight  := ord(getc(ppmFile));
          end for;
        end for;
      end if;
      close(ppmFile);
    end if;
  end func;

Tcl

Library: Tk

The actual PPM reader is built into the photo image engine:

package require Tk

proc readPPM {image file} {
    $image read $file -format ppm
}

Thus, to read a PPM, convert it to grayscale, and write it back out again becomes this (which requires Tcl 8.6 for try/finally); the PPM reader and writer are inlined because they are trivial at the script level:

package require Tk

proc grayscaleFile {filename {newFilename ""}} {
    set buffer [image create photo]
    if {$newFilename eq ""} {set newFilename $filename}
    try {
        $buffer read $filename -format ppm
        set w [image width $buffer]
        set h [image height $buffer]
        for {set x 0} {$x<$w} {incr x} {
            for {set y 0} {$y<$h} {incr y} {
                lassign [$buffer get $x $y] r g b
                set l [expr {int(0.2126*$r + 0.7152*$g + 0.0722*$b)}]
                $buffer put [format "#%02x%02x%02x" $l $l $l] -to $x $y
            }
        }
        $buffer write $newFilename -format ppm
    } finally {
        image delete $buffer
    }
}

However, the Tk library also has built-in the ability to convert code to grayscale directly during the saving of an image to a file, leading to this minimal solution:

package require Tk

proc grayscaleFile {filename {newFilename ""}} {
    set buffer [image create photo]
    if {$newFilename eq ""} {set newFilename $filename}
    try {
        $buffer read $filename -format ppm
        $buffer write $newFilename -format ppm -grayscale
    } finally {
        image delete $buffer
    }
}

UNIX Shell

Works with: ksh93

Ref: Bitmap#UNIX Shell

Add the following functions to the RGBColor_t type

    function setrgb {
        _.r=$1
        _.g=$2
        _.b=$3
    }
    function grayscale {
        integer x=$(( round( 0.2126*_.r + 0.7152*_.g + 0.0722*_.b ) ))
        _.r=$x
        _.g=$x
        _.b=$x
    }

Add the following function to the Bitmap_t type

    function grayscale {
        RGBColor_t c
        for ((y=0; y<_.height; y++)); do
            for ((x=0; x<_.width; x++)); do
                c.setrgb ${_.data[y][x]}
                c.grayscale
                _.data[y][x]=$(c.to_s)
            done
        done
    }

    function read {
        exec 4<"$1"
        typeset filetype
        read -u4 filetype
        if [[ $filetype != "P3" ]]; then
            print -u2 "error: I can only read P3 type PPM files"
        else
            read -u4 _.width _.height
            integer maxval
            read -u4 maxval
            integer x y r g b
            typeset -a bytes
            for ((y=0; y<_.height; y++)); do
                read -u4 -A bytes
                for ((x=0; x<_.width; x++)); do
                    r=${bytes[3*x+0]}
                    g=${bytes[3*x+1]}
                    b=${bytes[3*x+2]}
                    if (( r > maxval || g > maxval || b > maxval )); then
                        print -u2 "error: invalid color ($r $g $b), max=$maxval"
                        return 1
                    fi
                    _.data[y][x]="$r $g $b" 
                done 
            done
        fi
        exec 4<&-
    }

Now we can:

Bitmap_t c
c.read "$HOME/tmp/bitmap.ppm"
c.to_s

if [[ $(c.to_s) == $(cat "$HOME/tmp/bitmap.ppm") ]]; then
    echo looks OK
else
    echo something is wrong
fi

c.grayscale
c.to_s
c.write "$HOME/tmp/bitmap_g.ppm"

Vedit macro language

//   Load a PPM file
//     @10 = filename
//   On return:
//     #10 points to buffer containing pixel data,
//     #11 = width,  #12 = height.

:LOAD_PPM:
File_Open(@10)
BOF
Search("|X", ADVANCE)		// skip "P6"
#11 = Num_Eval(ADVANCE)		// #11 = width
Match("|X", ADVANCE)		// skip separator
#12 = Num_Eval(ADVANCE)		// #12 = height
Match("|X", ADVANCE)
Search("|X", ADVANCE)		// skip maxval (assume 255)
Del_Block(0,CP)			// remove the header
Return

Example of usage. In addition to LOAD_PPM routine above, you need routine RGB_TO_GRAYSCALE from Grayscale image and routine SAVE_PPM from Write ppm file.

// Load RGB image
Reg_Set(10, "|(USER_MACRO)\example.ppm")
Call("LOAD_PPM")

// Convert to grayscale
#10 = Buf_Num
Call("RGB_TO_GRAYSCALE")
Buf_Switch(#10) Buf_Quit(OK)

// Convert to RGB
Call("GRAYSCALE_TO_RGB")

// Save the image
Reg_Set(10, "|(USER_MACRO)\example_gray.ppm")
Call("SAVE_PPM")

// Cleanup and exit
Buf_Switch(#20) Buf_Quit(OK)
return

Wren

Library: DOME

This assumes that Lenna100.jpg, a 512 x 512 color image of the eponymous lady, has already been converted to Lenna100.ppm using a variation of the 'Write a PPM file' task.

import "graphics" for Canvas, ImageData, Color
import "dome" for Window, Process
import "io" for FileSystem

class Bitmap {
    construct new(fileName, fileName2, width, height) {
        Window.title = "Bitmap - read PPM file"
        Window.resize(width, height)
        Canvas.resize(width, height)
        _w = width
        _h = height
        _fn2 = fileName2
        loadPPMFile(fileName)
    }

    init() {
        toGrayScale()
        // display images side by side
        _bmp.draw(0, 0)
        _bmp2.draw(536, 0)
        // save gray scale image to file
        _bmp2.saveToFile(_fn2)
    }

    loadPPMFile(fileName) {
        var ppm = FileSystem.load(fileName)
        var count = ppm.count // ensure file is fully loaded before proceeding 
        if (ppm[0..1] != "P6") {
            System.print("The loaded file is not a P6 file.")
            Process.exit()
        }
        var lines = ppm.split("\n")
        if (Num.fromString(lines[2]) > 255) {
            System.print("The maximum color value can't exceed 255.")
            Process.exit()
        }
        var wh = lines[1].split(" ")
        var w = Num.fromString(wh[0])
        var h = Num.fromString(wh[1])
        _bmp = ImageData.create(fileName, w, h)
        var bytes = ppm.bytes
        var i = bytes.count - 3 * w * h
        for (y in 0...h) {
            for (x in 0...w) {
                var r = bytes[i]
                var g = bytes[i+1]
                var b = bytes[i+2]
                var c = Color.rgb(r, g, b)
                pset(x, y, c)
                i = i + 3
            }
        }
    }

    toGrayScale() {
        _bmp2 = ImageData.create("gray scale", _bmp.width, _bmp.height)
        for (x in 0..._bmp.width) {
            for (y in 0..._bmp.height) {
                var c1 = _bmp.pget(x, y)
                var lumin = (0.2126 * c1.r + 0.7152 * c1.g + 0.0722 * c1.b).floor
                var c2 = Color.rgb(lumin, lumin,lumin, c1.a)
                _bmp2.pset(x, y, c2)
            }
        }
    }

    pset(x, y, col) { _bmp.pset(x, y, col) }

    pget(x, y) { _bmp.pget(x, y) }

    update() {}

    draw(alpha) {}
}

var Game = Bitmap.new("Lenna100.ppm", "Lenna100_gs.jpg", 1048, 512)

XPL0

The simplicity of redirecting an input file on the command line doesn't work for files that contain binary data ($03 will abort a program). Image files larger than 1280x1024 are clipped to the screen dimensions.

include c:\cxpl\codes;          \intrinsic 'code' declarations

func OpenInFile;                \Open for input the file typed on command line
int  CpuReg, Handle;
char CmdTail($80);
[CpuReg:= GetReg;
Blit(CpuReg(11), $81, CpuReg(12), CmdTail, $7F);       \get copy of command line
Trap(false);                    \turn off error trapping
Handle:= FOpen(CmdTail, 0);     \open named file for input
FSet(Handle, ^I);               \assign file to input device 3
OpenI(3);                       \initialize input buffer pointers
if GetErr then return false;
Trap(true);
return true;
];

int  C, X, Y, Width, Height, Max, Lum;
real Red, Green, Blue;
[if not OpenInFile then [Text(0, "File not found");  exit];
if ChIn(3)#^P or ChIn(3)#^6 then [Text(0, "Not P6 PPM file");  exit];
repeat  loop    [C:= ChIn(3);
                if C # ^# then quit;
                repeat C:= ChIn(3) until C=$0A\EOL\;
                ];
until   C>=^0 & C<=^9;
Backup;                         \back up so IntIn re-reads first digit
Width:=  IntIn(3);              \(skips any whitespace)
Height:= IntIn(3);
Max:=    IntIn(3) + 1;          \(255/15=17; 256/16=16)
case of
  Width<= 640 & Height<=480: SetVid($112);
  Width<= 800 & Height<=600: SetVid($115);
  Width<=1024 & Height<=768: SetVid($118)
other SetVid($11B);             \1280x1024
for Y:= 0 to Height-1 do
    for X:= 0 to Width-1 do
        [Red  := float(ChIn(3)*256/Max) * 0.21; \convert color to grayscale
         Green:= float(ChIn(3)*256/Max) * 0.72;
         Blue := float(ChIn(3)*256/Max) * 0.07;
         Lum:= fix(Red) + fix(Green) + fix(Blue);
         Point(X, Y, Lum<<16 + Lum<<8 + Lum);
        ];
X:= ChIn(1);                    \wait for keystroke
SetVid(3);                      \restore normal text display
]

Yabasic

sub readPPM(f$)
	local ff, x, y, t$, dcol$, wid, hei

	if f$ = "" print "No PPM file name indicate." : return false

	ff = open (f$, "rb")
	if not ff print "File ", f$, " not found."  : return false

	input #ff t$, wid, hei, dcol$

	if t$ = "P6" then
		open window wid, hei
	
		for x = 0 to hei - 1
		 	for y = 0 to wid - 1
		 		color peek(#ff), peek(#ff), peek(#ff)
		 		dot y, x
		 	next y
		next x
		
		close #ff
	else
		print "File is NOT PPM P6 type." : return false
	end if
	
	return true
end sub

zkl

Translation of: FBSL

Read a colored PPM file, convert it (in place) to grayscale and write the new image back to disk under a different name. Sanity checks are omitted.

I used a slightly different image from what is shown, but the results are the same.

//24-bpp P6 PPM solution:
image:=File("lena.ppm","rb").read();
start:=image.find("\n255\n")+5;   // Get sizeof PPM header
 
foreach n in ([start..image.len()-1,3]){  //  Transform color triplets
   r,g,b:=image[n,3];  // Read colors stored in RGB order
   l:=(0.2126*r + 0.7152*g + 0.0722*b).toInt(); // Derive luminance
   image[n,3]=T(l,l,l);
}

File("lenaGrey.ppm","wb").write(image);