Sharpen filter?

Just thought I'd throw in a comment. I'd love to see a unsharp mask come (back) to image cache - it should be a core option in my opinion. Perhaps it needs to become it's own module? From the looks of it most of the heavy lifting has been done.

Okay, I should've looked a little closer before my last post. Here's a quick and dirty solution. I took the excellent code from the http://vikjavev.no/computing/ump.php site, slightly modified it, created a 'Custom Action' (custom php code) and voila. I attached a before/after image as an example.

The upside? Unsharp Mask! The downside? You have to enter the three unsharp mask values manually in the PHP code (the defaults are usually fine). Anyway, here's the code - remember to remove the PHP tags when pasting it into the Custom Action area:

////////////////////////////////////////////////////////////////////////////////////////////////  
////                  Unsharp Mask for PHP - version 2.1.1  
////    Unsharp mask algorithm by Torstein Hønsi 2003-07.  
////             thoensi_at_netcom_dot_no.  
///////////////////////////////////////////////////////////////////////////////////////////////   

	$img = $image->resource;
	$amount = '80'; // (Typically: 50 - 200 | Limits: .016 - 500 | Default: 80)
	$radius = '.5'; //	(Typically: 0.5 - 1 | Range: 0 - 50 | Default: .5)
	$threshold = '3'; // (Typically: 0 - 5 | Range: 0 - 255 | Default: 3)

    // 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;

Props go to Torstein Hønsi of course. This is all his code. Also thanks to the folks who brought us Imagecache and Imagecache Effects. Thank you!

There's a module to do sharpening: http://drupal.org/project/filtersie

See also: http://drupal.org/node/1056318