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);
}
imagewbmp
(PHP 4 >= 4.0.1, PHP 5)
imagewbmp — 輸出影像到瀏覽器或檔案。
說明
bool imagewbmp
( resource
$image
[, string $filename
[, int $foreground
]] )
imagewbmp() outputs or save a WBMP
version of the given image.
參數
-
image -
由影像建立函式(例如imagecreatetruecolor())回傳的影像資源。
-
filename -
檔案保存的路徑，如果未設置或為
NULL，將會直接輸出影像串流。 -
foreground -
You can set the foreground color with this parameter by setting an identifier obtained from imagecolorallocate(). The default foreground color is black.
回傳值
如果成功則回傳 TRUE，失敗則回傳 FALSE。
範例
Example #1 Outputting a WBMP image
<?php
// Create a blank image and add some text
$im = imagecreatetruecolor(120, 20);
$text_color = imagecolorallocate($im, 233, 14, 91);
imagestring($im, 1, 5, 5, 'A Simple Text String', $text_color);
// Set the content type header - in this case image/vnd.wap.wbmp
// Hint: see image_type_to_mime_type() for content-types
header('Content-Type: image/vnd.wap.wbmp');
// Output the image
imagewbmp($im);
// Free up memory
imagedestroy($im);
?>
Example #2 Saving the WBMP image
<?php
// Create a blank image and add some text
$im = imagecreatetruecolor(120, 20);
$text_color = imagecolorallocate($im, 233, 14, 91);
imagestring($im, 1, 5, 5, 'A Simple Text String', $text_color);
// Save the image
imagewbmp($im, 'simpletext.wbmp');
// Free up memory
imagedestroy($im);
?>
Example #3 Outputting the image with a different foreground
<?php
// Create a blank image and add some text
$im = imagecreatetruecolor(120, 20);
$text_color = imagecolorallocate($im, 233, 14, 91);
imagestring($im, 1, 5, 5, 'A Simple Text String', $text_color);
// Set the content type header - in this case image/vnd.wap.wbmp
// Hint: see image_type_to_mime_type() for content-types
header('Content-Type: image/vnd.wap.wbmp');
// Set a replacement foreground color
$foreground_color = imagecolorallocate($im, 255, 0, 0);
imagewbmp($im, NULL, $foreground_color);
// Free up memory
imagedestroy($im);
?>
註釋
Note:
WBMP support is only available if PHP was compiled against GD-1.8 or later.
參見
- image2wbmp() - 輸出影像到瀏覽器或檔案。
- imagepng() - Output a PNG image to either the browser or a file
- imagegif() - 輸出影像到瀏覽器或檔案。
- imagejpeg() - 輸出影像到瀏覽器或檔案。
- imagetypes() - Return the image types supported by this PHP build
add a note
User Contributed Notes 2 notes
andre at bynetworld dot com ¶
16 years ago
lukeross at sys3175 dot co dot uk ¶
22 years ago
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, use
ImageWBMP($final_img, "", ImageColorClosest(255,255,255));
