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, PHP 7, PHP 8)
imagewbmp — 输出图象到浏览器或文件。
说明
imagewbmp() 输出或保存为指定 image 的 WBMP 版本。
参数
-
image -
由图象创建函数(例如imagecreatetruecolor())返回的 GdImage 对象。
-
file -
文件保存的路径或者已打开的流资源（此方法返回后自动关闭该流资源），如果未设置或为
null，将会直接输出原始图象流。 -
foreground_color -
使用此参数从 imagecolorallocate() 获得的标识符来设置前景色。默认前景色为黑色。
返回值
成功时返回 true， 或者在失败时返回 false。
警告
如果 libgd 输出图像失败，函数会返回 true。
示例
示例 #1 输出 WBMP 图像
<?php
// 创建空白图像并添加文本
$im = imagecreatetruecolor(120, 20);
$text_color = imagecolorallocate($im, 233, 14, 91);
imagestring($im, 1, 5, 5, 'A Simple Text String', $text_color);
// 设置内容类型标头——在本例中是 image/vnd.wap.wbmp
// 提示，请参阅 image_type_to_mime_type() 了解内容类型
header('Content-Type: image/vnd.wap.wbmp');
// 输出图像
imagewbmp($im);
// 释放内存
imagedestroy($im);
?>
示例 #2 保存 WBMP 图像
<?php
// 创建空白图像并添加文本
$im = imagecreatetruecolor(120, 20);
$text_color = imagecolorallocate($im, 233, 14, 91);
imagestring($im, 1, 5, 5, 'A Simple Text String', $text_color);
// 保存图像
imagewbmp($im, 'simpletext.wbmp');
// 释放内存
imagedestroy($im);
?>
示例 #3 使用不同的前景色输出图像
<?php
// 创建空白图像并添加文本
$im = imagecreatetruecolor(120, 20);
$text_color = imagecolorallocate($im, 233, 14, 91);
imagestring($im, 1, 5, 5, 'A Simple Text String', $text_color);
// 设置内容类型标头——在本例中是 image/vnd.wap.wbmp
// 提示，请参阅 image_type_to_mime_type() 了解内容类型
header('Content-Type: image/vnd.wap.wbmp');
// 设置替换的前景色
$foreground_color = imagecolorallocate($im, 255, 0, 0);
imagewbmp($im, NULL, $foreground_color);
// 释放内存
imagedestroy($im);
?>参见
- image2wbmp() - 输出图象到浏览器或文件。
- imagepng() - 将 PNG 图像输出到浏览器或文件
- imagegif() - 输出图象到浏览器或文件。
- imagejpeg() - 输出图象到浏览器或文件。
- imagetypes() - 返回 PHP 内置支持的图像类型
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));
