Bitmap/Read an image through a pipe

From Rosetta Code

Bitmap/Read an image through a pipe is a programming task. Visitors like you are encouraged to solve it according to the task description, using any language they may happen to know.

This task is the opposite of the PPM conversion through a pipe. In this task, using a delegate tool (like cjpeg, one of the netpbm package, or convert of the ImageMagick package) we read an image file and load it into the data storage type defined here. We can also use the code from Read ppm file, so that we can use PPM format like a (natural) bridge between the foreign image format and our simple data storage.

[edit] C

Works with: POSIX version .1-2001 Here I've used convert by ImageMagick. It is up to the program to understand the source file type; in this way, we can read theoretically any image format ImageMagick can handle. The get_ppm function defined in Read ppm file is used.

image read_image(const char *name);

#include "imglib.h"
 
#define MAXCMDBUF 100
#define MAXFILENAMELEN 256
#define MAXFULLCMDBUF (MAXCMDBUF + MAXFILENAMELEN)
image read_image(const char *name)
{
      FILE *pipe;
      char buf[MAXFULLCMDBUF];
      image im;
 
      FILE *test = fopen(name, "r");
      if ( test == NULL ) {
         fprintf(stderr, "cannot open file %s\n", name);
         return NULL;
      }
      fclose(test);
 
      snprintf(buf, MAXFULLCMDBUF, "convert \"%s\" ppm:-", name);
      pipe = popen(buf, "r");
      if ( pipe != NULL )
      {
           im = get_ppm(pipe);
           pclose(pipe);
           return im;
      }
      return NULL;
}

[edit] OCaml

The read_ppm function of the page read ppm file and used by the code below would need to be changed to take as parameter an input channel instead of the filename.

let read_image ~filename =
  if not(Sys.file_exists filename)
  then failwith(Printf.sprintf "the file %s does not exist" filename);
  let cmd = Printf.sprintf "convert \"%s\" ppm:-" filename in
  let ic, oc = Unix.open_process cmd in
  let img = read_ppm ~ic in
  (img)
;;

[edit] Ruby

Extending Read ppm file#Ruby and PPM conversion through a pipe#Ruby. Uses the ImageMagick convert tool.

class Pixmap
  def self.read_ppm(ios)
    format = ios.gets.chomp
    width, height = ios.gets.chomp.split.map {|n| n.to_i }
    max_colour = ios.gets.chomp
 
    if (not PIXMAP_FORMATS.include?(format)) or 
        width < 1 or height < 1 or
        max_colour != '255'
    then
      ios.close
      raise StandardError, "file '#{filename}' does not start with the expected header"
    end
    ios.binmode if PIXMAP_BINARY_FORMATS.include?(format)
 
    bitmap = self.new(width, height)
    height.times do |y|
      width.times do |x|
        # read 3 bytes
        red, green, blue = case format
          when 'P3' then ios.gets.chomp.split
          when 'P6' then ios.read(3).unpack('C3')
        end
        bitmap[x,y] = RGBColour.new(red, green, blue)
      end
    end
    ios.close
    bitmap
  end
 
  def self.open(filename)
    read_ppm(File.open(filename, 'r'))
  end
 
  def self.open_from_jpeg(filename)
    read_ppm(IO.popen("convert jpg:#{filename} ppm:-", 'r'))
  end
end
 
bitmap = Pixmap.open_from_jpeg('file.jpg')

[edit] Tcl

Works with: Tcl version 8.6 Library: Tk

package require Tk
 
proc magickalReadImage {bufferImage fileName} {
    set f [open |[list convert [file normalize $fileName] ppm:-] "rb"]
    try {
        $bufferImage put [read $f] -format ppm
    } finally {
        close $f
    }
}