= 5.1, which improves the performance considerably. Unsharp masking is a traditional darkroom technique that has proven very suitable for digital imaging. The principle of unsharp masking is to create a blurred copy of the image and compare it to the underlying original. The difference in colour values between the two images is greatest for the pixels near sharp edges. When this difference is subtracted from the original image, the edges will be accentuated. The Amount parameter simply says how much of the effect you want. 100 is 'normal'. Radius is the radius of the blurring circle of the mask. 'Threshold' is the least difference in colour values that is allowed between the original and the mask. In practice this means that low-contrast areas of the picture are left unrendered whereas edges are treated normally. This is good for pictures of e.g. skin or blue skies. Any suggenstions for improvement of the algorithm, expecially regarding the speed and the roundoff errors in the Gaussian blur process, are welcome. */ $ThumbList['fProcessGD'] = 'UnsharpMask'; function UnsharpMask($img, $amount=100, $radius=5, $threshold=3) { //////////////////////////////////////////////////////////////////////////////////////////////// //// //// Unsharp Mask for PHP - version 2.1.1 //// //// Unsharp mask algorithm by Torstein Hønsi 2003-07. //// thoensi_at_netcom_dot_no. //// 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 $img; imagedestroy($img); break; } $w = imagesx($img); $h = imagesy($img); $imgCanvas = imagecreatetruecolor($w, $h); $imgBlur = imagecreatetruecolor($w, $h); // Gaussian blur matrix: // // 1 2 1 // 2 4 2 // 1 2 1 // ////////////////////////////////////////////////// if (function_exists('imageconvolution')) { // PHP >= 5.1 $matrix = array( array( 1, 2, 1 ), array( 2, 4, 2 ), array( 1, 2, 1 ) ); imagecopy ($imgBlur, $img, 0, 0, 0, 0, $w, $h); imageconvolution($imgBlur, $matrix, 16, 0); } else { // Move copies of the image around one pixel at the time and merge them with weight // according to the matrix. The same matrix is simply repeated for higher radii. for ($i = 0; $i < $radius; $i++) { imagecopy ($imgBlur, $img, 0, 0, 1, 0, $w - 1, $h); // left imagecopymerge ($imgBlur, $img, 1, 0, 0, 0, $w, $h, 50); // right imagecopymerge ($imgBlur, $img, 0, 0, 0, 0, $w, $h, 50); // center imagecopy ($imgCanvas, $imgBlur, 0, 0, 0, 0, $w, $h); imagecopymerge ($imgBlur, $imgCanvas, 0, 0, 0, 1, $w, $h - 1, 33.33333 ); // up imagecopymerge ($imgBlur, $imgCanvas, 0, 1, 0, 0, $w, $h, 25); // down } } if($threshold>0){ // Calculate the difference between the blurred pixels and the original // and set the pixels for ($x = 0; $x < $w-1; $x++) { // each row for ($y = 0; $y < $h; $y++) { // each pixel $rgbOrig = ImageColorAt($img, $x, $y); $rOrig = (($rgbOrig >> 16) & 0xFF); $gOrig = (($rgbOrig >> 8) & 0xFF); $bOrig = ($rgbOrig & 0xFF); $rgbBlur = ImageColorAt($imgBlur, $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, $pixCol); } } } } else{ for ($x = 0; $x < $w; $x++) { // each row for ($y = 0; $y < $h; $y++) { // each pixel $rgbOrig = ImageColorAt($img, $x, $y); $rOrig = (($rgbOrig >> 16) & 0xFF); $gOrig = (($rgbOrig >> 8) & 0xFF); $bOrig = ($rgbOrig & 0xFF); $rgbBlur = ImageColorAt($imgBlur, $x, $y); $rBlur = (($rgbBlur >> 16) & 0xFF); $gBlur = (($rgbBlur >> 8) & 0xFF); $bBlur = ($rgbBlur & 0xFF); $rNew = ($amount * ($rOrig - $rBlur)) + $rOrig; if($rNew>255){$rNew=255;} elseif($rNew<0){$rNew=0;} $gNew = ($amount * ($gOrig - $gBlur)) + $gOrig; if($gNew>255){$gNew=255;} elseif($gNew<0){$gNew=0;} $bNew = ($amount * ($bOrig - $bBlur)) + $bOrig; if($bNew>255){$bNew=255;} elseif($bNew<0){$bNew=0;} $rgbNew = ($rNew << 16) + ($gNew <<8) + $bNew; ImageSetPixel($img, $x, $y, $rgbNew); } } } imagedestroy($imgCanvas); imagedestroy($imgBlur); return $img; }