Grayscale image
From Rosetta Code
You are encouraged to solve this task according to the task description, using any language you may know.
Many image processing algorithms are defined for grayscale (or else monochromatic) images. Extend the data storage type defined on this page to support grayscale images. Define two operations, one to convert a color image to a grayscale image and one for the backward conversion. To get luminance of a color use the formula recommended by CIE:
L = 0.2126·R + 0.7152·G + 0.0722·B
When using floating-point arithmetic make sure that rounding errors would not cause run-time problems or else distorted results when calculated luminance is stored as an unsigned integer.
Contents |
[edit] Ada
type Grayscale_Image is array (Positive range <>, Positive range <>) of Luminance;
Conversion to a grayscale image:
function Grayscale (Picture : Image) return Grayscale_Image is
type Extended_Luminance is range 0..10_000_000;
Result : Grayscale_Image (Picture'Range (1), Picture'Range (2));
Color : Pixel;
begin
for I in Picture'Range (1) loop
for J in Picture'Range (2) loop
Color := Picture (I, J);
Result (I, J) :=
Luminance
( ( 2_126 * Extended_Luminance (Color.R)
+ 7_152 * Extended_Luminance (Color.G)
+ 722 * Extended_Luminance (Color.B)
)
/ 10_000
);
end loop;
end loop;
return Result;
end Grayscale;
Conversion to a color image:
function Color (Picture : Grayscale_Image) return Image is
Result : Image (Picture'Range (1), Picture'Range (2));
begin
for I in Picture'Range (1) loop
for J in Picture'Range (2) loop
Result (I, J) := (others => Picture (I, J));
end loop;
end loop;
return Result;
end Color;
[edit] C
Definition/interface for a grayscale image.
typedef unsigned char luminance;
typedef luminance pixel1[1];
typedef struct {
unsigned int width;
unsigned int height;
luminance *buf;
} grayimage_t;
typedef grayimage_t *grayimage;
grayimage alloc_grayimg(unsigned int, unsigned int);
grayimage tograyscale(image);
image tocolor(grayimage);
The same as alloc_img, but for grayscale images.
grayimage alloc_grayimg(unsigned int width, unsigned int height)
{
grayimage img;
img = malloc(sizeof(grayimage_t));
img->buf = malloc(width*height*sizeof(pixel1));
img->width = width;
img->height = height;
return img;
}
Convert from color image to grayscale image.
grayimage tograyscale(image img)
{
unsigned int x, y;
grayimage timg;
double rc, gc, bc, l;
unsigned int ofs;
timg = alloc_grayimg(img->width, img->height);
for(x=0; x < img->width; x++)
{
for(y=0; y < img->height; y++)
{
ofs = (y * img->width) + x;
rc = (double) img->buf[ofs][0];
gc = (double) img->buf[ofs][1];
bc = (double) img->buf[ofs][2];
l = 0.2126*rc + 0.7152*gc + 0.0722*bc;
timg->buf[ofs][0] = (luminance) (l+0.5);
}
}
return timg;
}
And back from a grayscale image to a color image.
image tocolor(grayimage img)
{
unsigned int x, y;
image timg;
luminance l;
unsigned int ofs;
timg = alloc_img(img->width, img->height);
for(x=0; x < img->width; x++)
{
for(y=0; y < img->height; y++)
{
ofs = (y * img->width) + x;
l = img->buf[ofs][0];
timg->buf[ofs][0] = l;
timg->buf[ofs][1] = l;
timg->buf[ofs][2] = l;
}
}
return timg;
}
Notes
- tocolor and tograyscale do not free the previous image, so it must be freed normally calling free_img. With a cast we can use the same function also for grayscale images, or we can define something like
#define free_grayimg(IMG) free_img((image)(IMG))
- Luminance is rounded. Since the C implementation is based on unsigned char (256 possible values per components), L can be at most 255.0 and rounding gives 255, as we expect. Changing the color_component type would only change 256, 255.0 and 255 values here written in something else, the code would work the same.
[edit] C#
To convert TO grayscale:
Bitmap tImage = new Bitmap("spectrum.bmp");
for (int x = 0; x < tImage.Width; x++)
{
for (int y = 0; y < tImage.Height; y++)
{
Color tCol = tImage.GetPixel(x, y);
// L = 0.2126·R + 0.7152·G + 0.0722·B
double L = 0.2126 * tCol.R + 0.7152 * tCol.G + 0.0722 * tCol.B;
tImage.SetPixel(x, y, Color.FromArgb(Convert.ToInt32(L), Convert.ToInt32(L), Convert.ToInt32(L)));
}
}
// Save
tImage.Save("spectrum2.bmp");
[edit] D
This example uses Bitmap template as defined on Basic bitmap storage problem page.
struct Lumin {
ubyte[1] value;
void opCall(ubyte l) { value[0] = l; }
void opCall(ubyte[1] v) { value[] = v[]; }
ubyte l() { return value[0]; }
}
alias Bitmap!(Lumin) GrayBitmap;
GrayBitmap rgbToGray(RgbBitmap bitmap) {
auto gb = GrayBitmap(bitmap.width, bitmap.height);
int x, y;
foreach (ref elem; gb) {
elem(bitmap[x, y].lumAVG);
if (++x == bitmap.width) { x = 0; y++; }
}
return gb;
}
RgbBitmap grayToRgb(GrayBitmap gray) {
auto rgb = RgbBitmap(gray.width, gray.height);
int x, y;
foreach (ref elem; rgb) {
elem(gray[x, y].l);
if (++x == gray.width) { x = 0; y++; }
}
return rgb;
}
Adding the following opCall methods to Lumin and Rgb structs
would allow to create simple conversion function template instead of two separate functions.
//in Rgb struct:
void opCall(Rgb v) { value[] = v.value[]; }
//in Lumin struct:
void opCall(Lumin l) { value[] = l.value[]; }
Conversion function template:
Bitmap!(TO) convert(FR, TO)(Bitmap!(FR) source, TO delegate(FR) dg) {
auto dest = Bitmap!(TO)(source.width, source.height);
int x, y;
foreach (ref elem; dest) {
elem( dg(source[x, y]) );
if (++x == source.width) { x = 0; y++; }
}
return dest;
}
Sample usage of conversion function:
// assuming t0 is of RgbBitmap type..
// convert RgbBitmap to GrayBitmap
auto t1 = convert(t0, delegate Lumin(Rgb v) { Lumin res; res(cast(ubyte)(0.2126*v.r + 0.7152*v.g + 0.0722*v.b)); return res; } );
// convert Graybitmap to grayscale - RgbBitmap
auto t2 = convert(t1, delegate Rgb(Lumin v) { Rgb res; res(v.l); return res; });
[edit] Euphoria
function to_gray(sequence image)
sequence color
for i = 1 to length(image) do
for j = 1 to length(image[i]) do
color = and_bits(image[i][j], {#FF0000,#FF00,#FF}) /
{#010000,#0100,#01} -- unpack color triple
image[i][j] = floor(0.2126*color[1] + 0.7152*color[2] + 0.0722*color[3])
end for
end for
return image
end function
function to_color(sequence image)
for i = 1 to length(image) do
for j = 1 to length(image[i]) do
image[i][j] = image[i][j]*#010101
end for
end for
return image
end function
[edit] Forth
\ grayscale bitmap (without word-alignment for scan lines)
\ bdim, bwidth, bdata all work with graymaps
: graymap ( w h -- gmp )
2dup * bdata allocate throw
dup >r 2! r> ;
: gxy ( x y gmp -- addr )
dup bwidth rot * rot + swap bdata + ;
: g@ ( x y gmp -- c ) gxy c@ ;
: g! ( c x y bmp -- ) gxy c! ;
: gfill ( c gmp -- )
dup bdata swap bdim * rot fill ;
: gshow ( gmp -- )
dup bdim
0 do cr
dup 0 do
over i j rot g@ if [char] * emit else space then
loop
loop
2drop ;
\ RGB <-> Grayscale
: lum>rgb ( 0..255 -- pixel )
dup 8 lshift or
dup 8 lshift or ;
: pixel>rgb ( pixel -- r g b )
256 /mod 256 /mod ;
: rgb>lum ( pixel -- 0..255 )
pixel>rgb
722 * swap
7152 * + swap
2126 * + 10000 / ;
: bitmap>graymap ( bmp -- gmp )
dup bdim graymap
dup bdim nip 0 do
dup bwidth 0 do
over i j rot b@ rgb>lum
over i j rot g!
loop
loop nip ;
: graymap>bitmap ( gmp -- bmp )
dup bdim bitmap
dup bdim nip 0 do
dup bwidth 0 do
over i j rot g@ lum>rgb
over i j rot b!
loop
loop nip ;
[edit] Fortran
(These fragments should be added to RCImageBasic module, see Basic bitmap storage)
First let's define a new type; the sc stands for Single Channel, which can be luminance (as it is here).
type scimage
integer, dimension(:,:), pointer :: channel
integer :: width, height
end type scimage
In order to allow proper overloading, the following subroutines of the storage should be renamed appending the _rgb suffix: valid_image, inside_image, alloc_img, free_img, fill_img, get_pixel, put_pixel, init_img. The single channel version would be named with the _sc suffix, then we should define the proper interfaces to use the already written code as before. Here there are only the interfaces and subroutines needed for the task.
interface alloc_img
module procedure alloc_img_rgb, alloc_img_sc
end interface
interface free_img
module procedure free_img_rgb, free_img_sc
end interface
Now we can define useful interfaces and subroutines more task-related:
interface assignment(=)
module procedure rgbtosc, sctorgb
end interface
subroutine alloc_img_sc(img, w, h)
type(scimage) :: img
integer, intent(in) :: w, h
allocate(img%channel(w, h))
img%width = w
img%height = h
end subroutine alloc_img_sc
subroutine free_img_sc(img)
type(scimage) :: img
if ( associated(img%channel) ) deallocate(img%channel)
end subroutine free_img_sc
subroutine rgbtosc(sc, colored)
type(rgbimage), intent(in) :: colored
type(scimage), intent(inout) :: sc
if ( ( .not. valid_image(sc) ) .and. valid_image(colored) ) then
call alloc_img(sc, colored%width, colored%height)
end if
if ( valid_image(sc) .and. valid_image(colored) ) then
sc%channel = floor(0.2126*colored%red + 0.7152*colored%green + &
0.0722*colored%blue)
end if
end subroutine rgbtosc
subroutine sctorgb(colored, sc)
type(scimage), intent(in) :: sc
type(rgbimage), intent(inout) :: colored
if ( ( .not. valid_image(colored) ) .and. valid_image(sc) ) then
call alloc_img_rgb(colored, sc%width, sc%height)
end if
if ( valid_image(sc) .and. valid_image(colored) ) then
colored%red = sc%channel
colored%green = sc%channel
colored%blue = sc%channel
end if
end subroutine sctorgb
Usage example (fragment) which can be used to convert from rgb image to grayscale image and back (since we only can output the rgb kind):
type(scimage) :: gray
type(rgbimage) :: animage
! ... here we "load" or create animage
! while gray must be created or initialized to null
! or errors can arise...
call init_img(gray)
gray = animage
animage = gray
call output_ppm(an_unit, animage)
[edit] Go
package raster
import (
"math"
"math/rand"
)
// Grmap parallels Bitmap, but with an element type of uint16
// in place of Pixel.
type Grmap struct {
Comments []string
rows, cols int
px []uint16
pxRow [][]uint16
}
// NewGrmap constructor.
func NewGrmap(x, y int) (b *Grmap) {
g := &Grmap{
Comments: []string{creator}, // creator a const in bitmap source file
rows: y,
cols: x,
px: make([]uint16, x*y),
pxRow: make([][]uint16, y),
}
x0, x1 := 0, x
for i := range g.pxRow {
g.pxRow[i] = g.px[x0:x1]
x0, x1 = x1, x1+x
}
return g
}
func (b *Grmap) Extent() (cols, rows int) {
return b.cols, b.rows
}
func (g *Grmap) Fill(c uint16) {
for i := range g.px {
g.px[i] = c
}
}
func (g *Grmap) SetPx(x, y int, c uint16) bool {
defer func() { recover() }()
g.pxRow[y][x] = c
return true
}
func (g *Grmap) GetPx(x, y int) (uint16, bool) {
defer func() { recover() }()
return g.pxRow[y][x], true
}
// Grmap method of Bitmap, converts (color) Bitmap to (grayscale) Grmap
func (b *Bitmap) Grmap() *Grmap {
g := NewGrmap(b.cols, b.rows)
g.Comments = append([]string{}, b.Comments...)
for i, p := range b.px {
g.px[i] = uint16((int64(p.R)*2126 + int64(p.G)*7152 + int64(p.B)*722) *
math.MaxUint16 / (math.MaxUint8 * 10000))
}
return g
}
// Bitmap method Grmap, converts Grmap to Bitmap. All pixels in the resulting
// color Bitmap will be (very nearly) shades of gray.
func (g *Grmap) Bitmap() *Bitmap {
b := NewBitmap(g.cols, g.rows)
b.Comments = append([]string{}, g.Comments...)
for i, p := range g.px {
roundedSum := int(p) * 3 * math.MaxUint8 / math.MaxUint16
rounded := uint8(roundedSum / 3)
remainder := roundedSum % 3
b.px[i].R = rounded
b.px[i].G = rounded
b.px[i].B = rounded
if remainder > 0 {
odd := rand.Intn(3)
switch odd + (remainder * 3) {
case 3:
b.px[i].R++
case 4:
b.px[i].G++
case 5:
b.px[i].B++
case 6:
b.px[i].G++
b.px[i].B++
case 7:
b.px[i].R++
b.px[i].B++
case 8:
b.px[i].R++
b.px[i].G++
}
}
}
return b
}
For demonstration program see task Bitmap/Read a PPM file.
[edit] Haskell
module Bitmap.Gray(module Bitmap.Gray) where
import Bitmap
import Control.Monad.ST
newtype Gray = Gray Int deriving (Eq, Ord)
instance Color Gray where
luminance (Gray x) = x
black = Gray 0
white = Gray 255
toNetpbm = map $ toEnum . luminance
fromNetpbm = map $ Gray . fromEnum
netpbmMagicNumber _ = "P5"
netpbmMaxval _ = "255"
toGrayImage :: Color c => Image s c -> ST s (Image s Gray)
toGrayImage = mapImage $ Gray . luminance
A Gray image can be converted to an RGB image with Bitmap.RGB.toRGBImage, defined here.
[edit] J
Color bitmap structure and basic functions for manipulations with it are described here.
Grayscale image is stored as two-dimensional array of luminance values. Allowed luminance scale is the same as for the color bitmap; the functions below are neutral to scale.
NB. converts the image to grayscale according to formula
NB. L = 0.2126*R + 0.7152*G + 0.0722*B
toGray=: [: <. +/ .*"1&0.2126 0.7152 0.0722
NB. converts grayscale image to the color image, with all channels equal
toColor=: 3 & $"0
Example:
viewRGB toColor toGray myimg
[edit] Java
void convertToGrayscale(final BufferedImage image){
for(int i=0; i<image.getWidth(); i++){
for(int j=0; j<image.getHeight(); j++){
int color = image.getRGB(i,j);
int alpha = (color >> 24) & 255;
int red = (color >> 16) & 255;
int green = (color >> 8) & 255;
int blue = (color) & 255;
final int lum = (int)(0.2126 * red + 0.7152 * green + 0.0722 * blue);
alpha = (alpha << 24);
red = (lum << 16);
green = (lum << 8);
blue = lum;
color = alpha + red + green + blue;
image.setRGB(i,j,color);
}
}
}
[edit] JavaScript
Live Demo: http://jsfiddle.net/J4zVy/embedded/result/.
To load local files into the canvas you have to run a local webserver. See: http://stackoverflow.com/questions/3276072/canvas-getimagedata-uncaught-error-security-err-dom-exception-18.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html><head><script type="text/javascript">
window.addEventListener(
"load", function(){
var img = new Image();
// ***********************************************************
// RUN LOCAL WEBSERVER TO LOAD LOCAL FILES: e.g. python -m http.server (python3)
// ***********************************************************
// img.src = prompt("enter image path","http://localhost:8000/test.jpg");
img.src =
'data:image/gif;base64,R0lGODlhEAAOALMAAOazToeHh0tLS/7LZv/0jvb29t/f3//Ub/\
/ge8WSLf/rhf/3kdbW1mxsbP//mf///yH5BAAAAAAALAAAAAAQAA4AAARe8L1Ekyky67QZ1hLnjM5UUde0ECwLJoExKcpp\
V0aCcGCmTIHEIUEqjgaORCMxIC6e0CcguWw6aFjsVMkkIr7g77ZKPJjPZqIyd7sJAgVGoEGv2xsBxqNgYPj/gAwXEQA7';
img.onload = function(){
var can1 = new CustomCanvas("color", img.width, img.height);
var can2 = new CustomCanvas("grayscale", img.width, img.height);
can1.ctx.drawImage(img,0, 0, img.width, img.height);
var imgData = can1.ctx.getImageData(0, 0, can1.w, can1.h);
// desaturate
var avg; var max; var rwgt=0.2126; var gwgt=0.7152; var bwgt=0.0722;
for(var i = 0, max = can1.w*can1.h*4; i < max; i=i+4){
avg = imgData.data[i]*rwgt + imgData.data[i+1]*gwgt + imgData.data[i+2]*bwgt;
imgData.data[i ] = avg; // red
imgData.data[i+1] = avg; // green
imgData.data[i+2] = avg;} // blue, alpha=alpha
can2.ctx.putImageData(imgData, 0, 0);
}
}, false);
function CustomCanvas(id, w, h, s) { /* Custom Canvas Object */
var c = document.createElement("canvas");
c.setAttribute('id', id); c.setAttribute('width', w);
c.setAttribute('height', h); (s)?c.setAttribute('style', s):0;
document.body.appendChild(c, document.body.firstChild);
this.ctx = document.getElementById(id).getContext("2d");
this.w = w; this.h = h;}
</script></head><body></body></html>
[edit] Lua
function ConvertToGrayscaleImage( bitmap )
local size_x, size_y = #bitmap, #bitmap[1]
local gray_im = {}
for i = 1, size_x do
gray_im[i] = {}
for j = 1, size_y do
gray_im[i][j] = math.floor( 0.2126*bitmap[i][j][1] + 0.7152*bitmap[i][j][2] + 0.0722*bitmap[i][j][3] )
end
end
return gray_im
end
function ConvertToColorImage( gray_im )
local size_x, size_y = #gray_im, #gray_im[1]
local bitmap = Allocate_Bitmap( size_x, size_y ) -- this function is defined at http://rosettacode.org/wiki/Basic_bitmap_storage#Lua
for i = 1, size_x do
for j = 1, size_y do
bitmap[i][j] = { gray_im[i][j], gray_im[i][j], gray_im[i][j] }
end
end
return bitmap
end
[edit] Mathematica
Mathematica has a built-in grayscale conversion function called "ColorConvert". This example does not use it since it appears the luminance calculation is different from the CIE spec. Grayscale to RGB "conversion" just changes the single channel grayscale image to a triple channel image.
toGrayscale[rgb_Image] := ImageApply[#.{0.2126, 0.7152, 0.0722}&, rgb]
toFakeRGB[L_Image] := ImageApply[{#, #, #}&, L]
[edit] MATLAB
Built in colour to grayscale converter uses the following forumula: 0.2989*R + 0.5870*G + 0.1140*B
function [grayImage] = colortograyscale(inputImage)
grayImage = rgb2gray(inputImage);
[edit] OCaml
Conversion to a grayscale image:
let to_grayscale ~img:(_, r_channel, g_channel, b_channel) =
let width = Bigarray.Array2.dim1 r_channel
and height = Bigarray.Array2.dim2 r_channel in
let gray_channel =
let kind = Bigarray.int8_unsigned
and layout = Bigarray.c_layout
in
(Bigarray.Array2.create kind layout width height)
in
for y = 0 to pred height do
for x = 0 to pred width do
let r = r_channel.{x,y}
and g = g_channel.{x,y}
and b = b_channel.{x,y} in
let v = (2_126 * r + 7_152 * g + 722 * b) / 10_000 in
gray_channel.{x,y} <- v;
done;
done;
(gray_channel)
Conversion to a color image:
let to_color ~img:gray_channel =
let width = Bigarray.Array2.dim1 gray_channel
and height = Bigarray.Array2.dim2 gray_channel in
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
Bigarray.Array2.blit gray_channel r_channel;
Bigarray.Array2.blit gray_channel g_channel;
Bigarray.Array2.blit gray_channel b_channel;
(all_channels,
r_channel,
g_channel,
b_channel)
and functions to get/set a pixel:
let gray_get_pixel_unsafe (gray_channel) =
(fun x y -> gray_channel.{x,y})
let gray_put_pixel_unsafe (gray_channel) v =
(fun x y -> gray_channel.{x,y} <- v)
[edit] Octave
Use package: image
function [grayImage] = colortograyscale(inputImage)
grayImage = rgb2gray(inputImage);
Differently from MATLAB, the grayscale is computed as mean of the three RGB values. Changing this non-optimal behaviour is a matter of fixing three lines in the rgb2gray.m file; since it's a GPL-ed code, here it is a semplified version (error checking, usage help, argument checking removed)
function gray = rgb2gray (rgb)
switch(class(rgb))
case "double"
gray = luminance(rgb);
case "uint8"
gray = uint8(luminance(rgb));
case "uint16"
gray = uint16(luminance(rgb));
endswitch
endfunction
function lum = luminance(rgb)
lum = 0.2126*rgb(:,:,1) + 0.7152*rgb(:,:,2) + 0.0722*rgb(:,:,3);
endfunction
Original code of the rgb2gray.m in the image package version 1.0.8 is by Kai Habel (under the GNU General Public License)
[edit] Oz
We define a "graymap" as a two-dimensional array of floats. In module "Grayscale.oz", we implement conversion functions from and to bitmaps:
functor
import
Array2D
export
ToGraymap
FromGraymap
define
fun {ToGraymap bitmap(Arr)}
graymap({Array2D.map Arr Luminance})
end
fun {Luminance Color}
F = {Record.map Color Int.toFloat}
in
0.2126*F.1 + 0.7152*F.2 + 0.0722*F.3
end
fun {FromGraymap graymap(Arr)}
bitmap({Array2D.map Arr ToColor})
end
fun {ToColor Lum}
L = {Float.toInt Lum}
in
color(L L L)
end
end
[edit] Perl
Since we are using Imlib2, this one does not implement really a gray-scale (single channel) storage; it only converts an RGB image to an RGB image with the same three colour components for each pixel (which result in a gray-scale-like image)
#! /usr/bin/perl
use strict;
use Image::Imlib2;
sub tograyscale
{
my $img = shift;
my $gimg = Image::Imlib2->new($img->width, $img->height);
for ( my $x = 0; $x < $gimg->width; $x++ ) {
for ( my $y = 0; $y < $gimg->height; $y++ ) {
my ( $r, $g, $b, $a ) = $img->query_pixel($x, $y);
my $gray = int(0.2126 * $r + 0.7152 * $g + 0.0722 * $b);
# discard alpha info...
$gimg->set_color($gray, $gray, $gray, 255);
$gimg->draw_point($x, $y);
}
}
return $gimg;
}
my $animage = Image::Imlib2->load("Lenna100.jpg");
my $gscale = tograyscale($animage);
$gscale->set_quality(80);
$gscale->save("Lennagray.jpg");
exit 0;
[edit] Perl 6
This script expects to be fed a P6 .ppm file name at the command line. It will convert it to grey scale and save it as a binary portable grey map (P5 .pgm) file.
sub MAIN ($filename = 'default.ppm') {
my $in = open( $filename, :r , :bin ) or die "$!\n";
my ($type, $dim, $depth) = $in.lines[^3];
my $outfile = $filename.subst('.ppm', '.pgm');
my $out = open( $outfile, :w, :bin ) or die "$!\n";
$out.say("P5\n$dim\n$depth");
for $in.slurp.ords -> $r, $g, $b {
my $gs = $r * 0.2126 + $g * 0.7152 + $b * 0.0722;
$out.print: chr($gs min 255);
}
$in.close;
$out.close;
}
Using the .ppm file from the Write a PPM file task:
Original: 
Grey Scale: 
[edit] PHP
Uses the Bitmap class defined for writing a PPM file
class BitmapGrayscale extends Bitmap {
public function toGrayscale(){
for ($i = 0; $i < $this->h; $i++){
for ($j = 0; $j < $this->w; $j++){
$l = ($this->data[$j][$i][0] * 0.2126)
+ ($this->data[$j][$i][1] * 0.7152)
+ ($this->data[$j][$i][2] * 0.0722);
$l = round($l);
$this->data[$j][$i] = array($l,$l,$l);
}
}
}
}
$b = new BitmapGrayscale(16,16);
$b->fill(0,0,null,null, array(255,255,0));
$b->setPixel(0, 15, array(255,0,0));
$b->setPixel(0, 14, array(0,255,0));
$b->setPixel(0, 13, array(0,0,255));
$b->toGrayscale();
$b->writeP6('p6-grayscale.ppm');
[edit] PL/I
do j = 1 to hbound(image,1);
do i = 0 to hbound(image,2);
color = image(i,j);
R = substr(color, 17, 8);
G = substr(color, 9, 8);
B = substr(color, 1, 8);
grey = trunc(0.2126*R + 0.7152*G + 0.0722*B);
greybits = grey;
image(i,j) = substr(greybits, length(greybits)-7, 8);
end;
end;
[edit] PicoLisp
# Convert color image (PPM) to greyscale image (PGM)
(de ppm->pgm (Ppm)
(mapcar
'((Y)
(mapcar
'((C)
(/
(+
(* (car C) 2126) # Red
(* (cadr C) 7152) # Green
(* (caddr C) 722) ) # Blue
10000 ) )
Y ) )
Ppm ) )
# Convert greyscale image (PGM) to color image (PPM)
(de pgm->ppm (Pgm)
(mapcar
'((Y)
(mapcar
'((G) (list G G G))
Y ) )
Pgm ) )
# Write greyscale image (PGM) to file
(de pgmWrite (Pgm File)
(out File
(prinl "P5")
(prinl (length (car Pgm)) " " (length Pgm))
(prinl 255)
(for Y Pgm (apply wr Y)) ) )
# Create an empty image of 120 x 90 pixels
(setq *Ppm (make (do 90 (link (need 120)))))
# Fill background with green color
(ppmFill *Ppm 0 255 0)
# Draw a diagonal line
(for I 80 (ppmSetPixel *Ppm I I 0 0 0))
# Convert to greyscale image (PGM)
(setq *Pgm (ppm->pgm *Ppm))
# Write greyscale image to .pgm file
(pgmWrite *Pgm "img.pgm")
# Convert to color image and write to .ppm file
(ppmWrite (pgm->ppm *Pgm) "img.ppm")
[edit] PureBasic
Procedure ImageGrayout(image)
w = ImageWidth(image)
h = ImageHeight(image)
StartDrawing(ImageOutput(image))
For x = 0 To w - 1
For y = 0 To h - 1
color = Point(x, y)
r = color & $ff
g = color >> 8 & $ff
b = color >> 16 & $ff
gray = 0.2126*r + 0.7152*g + 0.0722*b
Plot(x, y, gray + gray << 8 + gray << 16)
Next
Next
StopDrawing()
EndProcedure
[edit] Python
Extending the example given here
# String masquerading as ppm file (version P3)
import io
ppmfileout = io.StringIO('')
def togreyscale(self):
for h in range(self.height):
for w in range(self.width):
r, g, b = self.get(w, h)
l = int(0.2126 * r + 0.7152 * g + 0.0722 * b)
self.set(w, h, Colour(l, l, l))
Bitmap.togreyscale = togreyscale
# Draw something simple
bitmap = Bitmap(4, 4, white)
bitmap.fillrect(1, 0, 1, 2, Colour(127, 0, 63))
bitmap.set(3, 3, Colour(0, 127, 31))
print('Colour:')
# Write to the open 'file' handle
bitmap.writeppmp3(ppmfileout)
print(ppmfileout.getvalue())
print('Grey:')
bitmap.togreyscale()
ppmfileout = io.StringIO('')
bitmap.writeppmp3(ppmfileout)
print(ppmfileout.getvalue())
'''
The print statement above produces the following output :
Colour:
P3
# generated from Bitmap.writeppmp3
4 4
255
255 255 255 255 255 255 255 255 255 0 127 31
255 255 255 255 255 255 255 255 255 255 255 255
255 255 255 127 0 63 255 255 255 255 255 255
255 255 255 127 0 63 255 255 255 255 255 255
Grey:
P3
# generated from Bitmap.writeppmp3
4 4
254
254 254 254 254 254 254 254 254 254 93 93 93
254 254 254 254 254 254 254 254 254 254 254 254
254 254 254 31 31 31 254 254 254 254 254 254
254 254 254 31 31 31 254 254 254 254 254 254
'''
[edit] R
# Conversion from Grey to RGB uses the following code
setAs("pixmapGrey", "pixmapRGB",
function(from, to){
z = new(to, as(from, "pixmap"))
z@red = from@grey
z@green = from@grey
z@blue = from@grey
z@channels = c("red", "green", "blue")
z
})
# Conversion from RGB to grey uses built-in coefficients of 0.3, 0.59, 0.11. To see this, type
getMethods(addChannels)
# We can override this behaviour with
setMethod("addChannels", "pixmapRGB",
function(object, coef=NULL){
if(is.null(coef)) coef = c(0.2126, 0.7152, 0.0722)
z = new("pixmapGrey", object)
z@grey = coef[1] * object@red + coef[2] * object@green +
coef[3] * object@blue
z@channels = "grey"
z
})
# Colour image
plot(p1 <- pixmapRGB(c(c(1,0,0,0,0,1), c(0,1,0,0,1,0), c(0,0,1,1,0,0)), nrow=6, ncol=6))
#Convert to grey
plot(p2 <- as(p1, "pixmapGrey"))
# Convert back to "colour"
plot(p3 <- as(p2, "pixmapRGB"))
[edit] REXX
/*REXX program to convert a RGB image to grayscale. */
blue='00 00 ff'x /*define the blue color. */
image.=blue /*set the entire IMAGE to blue. */
width= 60 /* width of the IMAGE. */
height=100 /*height " " " */
do j=1 for width
do k=1 for height
r= left(image.j.k,1) ; r=c2d(r) /*extract red & convert*/
g=substr(image.j.k,2,1) ; g=c2d(g) /* " green " " */
b= right(image.j.k,1) ; b=c2d(b) /* " blue " " */
ddd=right(trunc(.2126*r + .7152*g + .0722*b),3,0) /*──► greyscale.*/
image.j.k=right(d2c(ddd,6),3,0) /*... and transform back.*/
end
end
[edit] Ruby
Extending Basic_bitmap_storage#Ruby
class RGBColour
def to_grayscale
luminosity = Integer(0.2126*@red + 0.7152*@green + 0.0722*@blue)
self.class.new(luminosity, luminosity, luminosity)
end
end
class Pixmap
def to_grayscale
gray = self.class.new(@width, @height)
@width.times do |x|
@height.times do |y|
gray[x,y] = self[x,y].to_grayscale
end
end
gray
end
end
[edit] Scala
Uses the Scala Basic Bitmap Storage class.
object BitmapOps {
def luminosity(c:Color)=(0.2126*c.getRed + 0.7152*c.getGreen + 0.0722*c.getBlue+0.5).toInt
def grayscale(bm:RgbBitmap)={
val image=new RgbBitmap(bm.width, bm.height)
for(x <- 0 until bm.width; y <- 0 until bm.height; l=luminosity(bm.getPixel(x,y)))
image.setPixel(x, y, new Color(l,l,l))
image
}
}
[edit] Tcl
package require Tk
proc grayscale image {
set w [image width $image]
set h [image height $image]
for {set x 0} {$x<$w} {incr x} {
for {set y 0} {$y<$h} {incr y} {
lassign [$image get $x $y] r g b
set l [expr {int(0.2126*$r + 0.7152*$g + 0.0722*$b)}]
$image put [format "#%02x%02x%02x" $l $l $l] -to $x $y
}
}
}
Photo images are always 8-bits-per-channel RGBA.
[edit] Vedit macro language
Conversion to a grayscale image.
// Convert RGB image to grayscale (8 bit/pixel)
// #10 = buffer that contains image data
// On return:
// #20 = buffer for the new grayscale image
:RGB_TO_GRAYSCALE:
File_Open("|(VEDIT_TEMP)\gray.data", OVERWRITE+NOEVENT+NOMSG)
#20 = Buf_Num
BOF
Del_Char(ALL)
Buf_Switch(#10)
Repeat(File_Size/3) {
#9 = Cur_Char() * 2126
#9 += Cur_Char(1) * 7152
#9 += Cur_Char(2) * 722
Char(3)
Buf_Switch(#20)
Ins_Char(#9 / 10000)
Buf_Switch(#10)
}
Return
Conversion to a color image.
// Convert grayscale image (8 bits/pixel) into RGB (24 bits/pixel)
// #20 = buffer that contains image data
// On return:
// #10 = buffer for the new RGB image
:GRAYSCALE_TO_RGB:
File_Open("|(VEDIT_TEMP)\RGB.data", OVERWRITE+NOEVENT+NOMSG)
#10 = Buf_Num
BOF
Del_Char(ALL)
Buf_Switch(#20) // input image (grayscale)
BOF
Repeat(File_Size) {
#9 = Cur_Char()
Char
Buf_Switch(#10) // output image (RGB)
Ins_Char(#9, COUNT, 3)
Buf_Switch(#20)
}
Return
[edit] Visual Basic .NET
Convert a Bitmap to Grayscale.
Imports System.Drawing.Imaging
Public Function Grayscale(ByVal Map As Bitmap) As Bitmap
Dim oData() As Integer = GetData(Map)
Dim oReturn As New Bitmap(Map.Width, Map.Height, Map.PixelFormat)
Dim a As Integer = 0
Dim r As Integer = 0
Dim g As Integer = 0
Dim b As Integer = 0
Dim l As Integer = 0
For i As Integer = 0 To oData.GetUpperBound(0)
a = (oData(i) >> 24)
r = (oData(i) >> 16) And 255
g = (oData(i) >> 8) And 255
b = oData(i) And 255
l = CInt(r * 0.2126F + g * 0.7152F + b * 0.0722F)
oData(i) = (a << 24) Or (l << 16) Or (l << 8) Or l
Next
SetData(oReturn, oData)
Return oReturn
End Function
Private Function GetData(ByVal Map As Bitmap) As Integer()
Dim oBMPData As BitmapData = Nothing
Dim oData() As Integer = Nothing
oBMPData = Map.LockBits(New Rectangle(0, 0, Map.Width, Map.Height), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb)
Array.Resize(oData, Map.Width * Map.Height)
Runtime.InteropServices.Marshal.Copy(oBMPData.Scan0, oData, 0, oData.Length)
Map.UnlockBits(oBMPData)
Return oData
End Function
Private Sub SetData(ByVal Map As Bitmap, ByVal Data As Integer())
Dim oBMPData As BitmapData = Nothing
oBMPData = Map.LockBits(New Rectangle(0, 0, Map.Width, Map.Height), ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb)
Runtime.InteropServices.Marshal.Copy(Data, 0, oBMPData.Scan0, Data.Length)
Map.UnlockBits(oBMPData)
End Sub
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