function unsharp_mask($img, $amount, $radius, $threshold) {
/*
Unsharp Mask for PHP - version 2.0
Unsharp mask algorithm by Torstein H�nsi 2003-06.
Please leave this notice.
*/
// $img is an image that is already created within php using
// imgcreatetruecolor. No url! $img must be a truecolor image.
// Attempt to calibrate the parameters to Photoshop:
if ($amount > 500) $amount = 500;
$amount = $amount * 0.016;
if ($radius > 50) $radius = 50;
$radius = $radius * 2;
if ($threshold > 255) $threshold = 255;
$radius = abs(round($radius)); // Only integers make sense.
if ($radius == 0) return $img;
$w = imagesx($img); $h = imagesy($img);
$imgCanvas = imagecreatetruecolor($w, $h);
$imgCanvas2 = imagecreatetruecolor($w, $h);
$imgBlur = imagecreatetruecolor($w, $h);
$imgBlur2 = imagecreatetruecolor($w, $h);
imagecopy ($imgCanvas, $img, 0, 0, 0, 0, $w, $h);
imagecopy ($imgCanvas2, $img, 0, 0, 0, 0, $w, $h);
// Gaussian blur matrix:
// 1 2 1
// 2 4 2
// 1 2 1
//////////////////////////////////////////////////
imagecopy($imgBlur, $imgCanvas, 0, 0, 0, 0, $w, $h); // background
for ($i = 0; $i < $radius; $i++) {
if (function_exists('imageconvolution')) { // PHP >= 5.1
$matrix = array(
array( 1, 2, 1 ),
array( 2, 4, 2 ),
array( 1, 2, 1 )
);
imageconvolution($imgCanvas, $matrix, 16, 0);
} else {
// Move copies of the image around one pixel at the time and merge them with weight
// according to the matrix. The same matrix is simply repeated for higher radii.
imagecopy ($imgBlur, $imgCanvas, 0, 0, 1, 1, $w - 1, $h - 1); // up left
imagecopymerge ($imgBlur, $imgCanvas, 1, 1, 0, 0, $w, $h, 50); // down right
imagecopymerge ($imgBlur, $imgCanvas, 0, 1, 1, 0, $w - 1, $h, 33.33333); // down left
imagecopymerge ($imgBlur, $imgCanvas, 1, 0, 0, 1, $w, $h - 1, 25); // up right
imagecopymerge ($imgBlur, $imgCanvas, 0, 0, 1, 0, $w - 1, $h, 33.33333); // left
imagecopymerge ($imgBlur, $imgCanvas, 1, 0, 0, 0, $w, $h, 25); // right
imagecopymerge ($imgBlur, $imgCanvas, 0, 0, 0, 1, $w, $h - 1, 20 ); // up
imagecopymerge ($imgBlur, $imgCanvas, 0, 1, 0, 0, $w, $h, 16.666667); // down
imagecopymerge ($imgBlur, $imgCanvas, 0, 0, 0, 0, $w, $h, 50); // center
imagecopy ($imgCanvas, $imgBlur, 0, 0, 0, 0, $w, $h);
// During the loop above the blurred copy darkens, possibly due to a roundoff
// error. Therefore the sharp picture has to go through the same loop to
// produce a similar image for comparison. This is not a good thing, as processing
// time increases heavily.
imagecopy ($imgBlur2, $imgCanvas2, 0, 0, 0, 0, $w, $h);
imagecopymerge ($imgBlur2, $imgCanvas2, 0, 0, 0, 0, $w, $h, 50);
imagecopymerge ($imgBlur2, $imgCanvas2, 0, 0, 0, 0, $w, $h, 33.33333);
imagecopymerge ($imgBlur2, $imgCanvas2, 0, 0, 0, 0, $w, $h, 25);
imagecopymerge ($imgBlur2, $imgCanvas2, 0, 0, 0, 0, $w, $h, 33.33333);
imagecopymerge ($imgBlur2, $imgCanvas2, 0, 0, 0, 0, $w, $h, 25);
imagecopymerge ($imgBlur2, $imgCanvas2, 0, 0, 0, 0, $w, $h, 20 );
imagecopymerge ($imgBlur2, $imgCanvas2, 0, 0, 0, 0, $w, $h, 16.666667);
imagecopymerge ($imgBlur2, $imgCanvas2, 0, 0, 0, 0, $w, $h, 50);
imagecopy ($imgCanvas2, $imgBlur2, 0, 0, 0, 0, $w, $h);
}
}
// Calculate the difference between the blurred pixels and the original
// and set the pixels
for ($x = 0; $x < $w; $x++) { // each row
for ($y = 0; $y < $h; $y++) { // each pixel
$rgbOrig = ImageColorAt($imgCanvas2, $x, $y);
$rOrig = (($rgbOrig >> 16) & 0xFF);
$gOrig = (($rgbOrig >> 8) & 0xFF);
$bOrig = ($rgbOrig & 0xFF);
$rgbBlur = ImageColorAt($imgCanvas, $x, $y);
$rBlur = (($rgbBlur >> 16) & 0xFF);
$gBlur = (($rgbBlur >> 8) & 0xFF);
$bBlur = ($rgbBlur & 0xFF);
// When the masked pixels differ less from the original
// than the threshold specifies, they are set to their original value.
$rNew = (abs($rOrig - $rBlur) >= $threshold)
? max(0, min(255, ($amount * ($rOrig - $rBlur)) + $rOrig))
: $rOrig;
$gNew = (abs($gOrig - $gBlur) >= $threshold)
? max(0, min(255, ($amount * ($gOrig - $gBlur)) + $gOrig))
: $gOrig;
$bNew = (abs($bOrig - $bBlur) >= $threshold)
? max(0, min(255, ($amount * ($bOrig - $bBlur)) + $bOrig))
: $bOrig;
if (($rOrig != $rNew) || ($gOrig != $gNew) || ($bOrig != $bNew)) {
$pixCol = ImageColorAllocate($img, $rNew, $gNew, $bNew);
ImageSetPixel($img, $x, $y, $pixCol);
}
}
}
return $img;
}
