imagewbmp

In the previous note by -> lukeross at sys3175 dot co dot uk <- there is a coding error in the for() loops. After correcting the error, I found that this function did a great job of  converting color images to 2 colors.The following is the corrected function code:function ImageColorFloydSteinberg($dst_img, $src_img) {    ImageColorAllocate($dst_img, 0,0,0);    ImageColorAllocate($dst_img, 255,255,255);    $isx = ImageSX($src_img);    $isy = ImageSY($src_img);    $grey_img = ImageCreate($isx, $isy);    for ($a = 0; $a <= 255; $a++) ImageColorAllocate($grey_img, $a,$a,$a);    $isx -= 1; // To correct pixel count in source image width starting from 0    $isy -= 1; // Correcting pixel count in source image height starting from 0    for($x = 0; $x <= $isx; $x++) {        for($y = 0; $y <= $isy; $y++) {            $color = ImageColorsForIndex($src_img, ImageColorAt($src_img, $x, $y));            $greyscale = .299 * $color["red"] + .587 * $color["green"] + .114 * $color["blue"];            ImageSetPixel($grey_img, $x, $y, ImageColorClosest($grey_img, $greyscale, $greyscale, $greyscale));        }    }    for($x = 0; $x <= $isx; $x++) {        for($y = 0; $y <= $isy; $y++) {            $color = ImageColorsForIndex($grey_img, ImageColorAt($grey_img, $x, $y));            if ($color["red"] > 128) {                ImageSetPixel($dst_img, $x, $y, ImageColorClosest($dst_img,255,255,255));                $err = $color["red"] - 255;            } else {                ImageSetPixel($dst_img, $x, $y, ImageColorClosest($dst_img,0,0,0));                $err = $color["red"];            }            if ($x != $isx) {                $color2 = ImageColorsForIndex($grey_img, ImageColorAt($grey_img, $x+1, $y));                $newgrey = $color2["red"] + $err * 7 / 16;                ImageSetPixel($grey_img, $x+1, $y, ImageColorClosest($grey_img,$newgrey, $newgrey, $newgrey));            }            if ($x != 0) {                $color2 = ImageColorsForIndex($grey_img, ImageColorAt($grey_img, $x-1, $y));                $newgrey = $color2["red"] + $err * 3 / 16;                ImageSetPixel($grey_img, $x-1, $y, ImageColorClosest($grey_img,$newgrey, $newgrey, $newgrey));            }            if ($y != $isy) {                $color2 = ImageColorsForIndex($grey_img, ImageColorAt($grey_img, $x, $y+1));                $newgrey = $color2["red"] + $err * 5 / 16;                ImageSetPixel($grey_img, $x, $y+1, ImageColorClosest($grey_img,$newgrey, $newgrey, $newgrey));            }            if ($x != $isx && $y != $isy) {                $color2 = ImageColorsForIndex($grey_img, ImageColorAt($grey_img, $x+1, $y+1));                $newgrey = $color2["red"] + $err / 16;                ImageSetPixel($grey_img, $x+1, $y+1, ImageColorClosest($grey_img,$newgrey, $newgrey, $newgrey));            }                   }    }    imagedestroy($grey_img);}

As has been commented before, GD doesnt do a very good translation to 2-colours, especially for photos.  The following routine converts to two colours, I believe using error diffusion (the algorithm's nicked off news).  It's slow, but just about adequate for small images and low load.  I suspect it can be made much more efficient :-)function ImageColorFloydSteinberg($dst_img, $src_img) {    ImageColorAllocate($dst_img, 0,0,0);    ImageColorAllocate($dst_img, 255,255,255);    $grey_img = ImageCreate(ImageSX($src_img), ImageSY($src_img));    for ($a = 0; $a <= 255; $a++) ImageColorAllocate($grey_img, $a,$a,$a);    for($x = 0; $x <= ImageSX($src_img); $x++) {        for($y = 0; $y <= ImageSY($src_img); $y++) {            $color = ImageColorsForIndex($src_img, ImageColorAt($src_img, $x, $y));            $greyscale = .299 * $color["red"] + .587 * $color["green"] + .114 * $color["blue"];            ImageSetPixel($grey_img, $x, $y, ImageColorClosest($grey_img, $greyscale, $greyscale, $greyscale));        }    }    for($x = 0; $x <= ImageSX($src_img); $x++) {        for($y = 0; $y <= ImageSY($src_img); $y++) {            $color = ImageColorsForIndex($grey_img, ImageColorAt($grey_img, $x, $y));            if ($color["red"] > 128) {                ImageSetPixel($dst_img, $x, $y, ImageColorClosest($dst_img,255,255,255));                $err = $color["red"] - 255;            } else {                ImageSetPixel($dst_img, $x, $y, ImageColorClosest($dst_img,0,0,0));                $err = $color["red"];            }            if ($x != ImageSx($src_img)) {                $color2 = ImageColorsForIndex($grey_img, ImageColorAt($grey_img, $x+1, $y));                $newgrey = $color2["red"] + $err * 7 / 16;                ImageSetPixel($grey_img, $x+1, $y, ImageColorClosest($grey_img,$newgrey, $newgrey, $newgrey));            }            if ($x != 0) {                $color2 = ImageColorsForIndex($grey_img, ImageColorAt($grey_img, $x-1, $y));                $newgrey = $color2["red"] + $err * 3 / 16;                ImageSetPixel($grey_img, $x-1, $y, ImageColorClosest($grey_img,$newgrey, $newgrey, $newgrey));            }            if ($y != ImageSy($src_img)) {                $color2 = ImageColorsForIndex($grey_img, ImageColorAt($grey_img, $x, $y+1));                $newgrey = $color2["red"] + $err * 5 / 16;                ImageSetPixel($grey_img, $x, $y+1, ImageColorClosest($grey_img,$newgrey, $newgrey, $newgrey));            }            if ($x != ImageSx($src_img) && $y != ImageSy($src_img)) {                $color2 = ImageColorsForIndex($grey_img, ImageColorAt($grey_img, $x+1, $y+1));                $newgrey = $color2["red"] + $err / 16;                ImageSetPixel($grey_img, $x+1, $y+1, ImageColorClosest($grey_img,$newgrey, $newgrey, $newgrey));            }                    }    }    imagedestroy($grey_img);}To output your WBMP, useImageWBMP($final_img, "", ImageColorClosest(255,255,255));