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POTransforming transparent `gif` to grayscale while saving transparency
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copied!<p>First, I resize the image while saving transparency:</p> <pre><code>/* all the classic routine etcetera: $canvas = imagecreatefrom[png|gif|jpeg](); $resize = imagecreatetruecolor(); */ if($blending){ $transparentIndex = imagecolortransparent($canvas); if($transparentIndex >= 0){ #GIF imagepalettecopy($canvas, $resize); imagefill($resize, 0, 0, $transparentIndex); imagecolortransparent($resize, $transparentIndex); imagetruecolortopalette($resize, true, 256); }else{ #PNG imagealphablending($resize, false); imagesavealpha($resize, true); $transparent = imagecolorallocatealpha($resize, 255, 255, 255, 127); imagefill($resize, 0, 0, $transparent); } } imagecopyresampled($resize, $canvas, 0, 0, 0, 0, $nx, $ny, $x, $y); // image[png|gif|jpeg]... (image gets saved) </code></pre> <p>Then, I want to apply grayscale filter to that previously saved image (within a new function):</p> <pre><code>/* classic routine again: $canvas = imagecreatefrom[png|gif|jpeg]() */ if($blending){ imagealphablending($canvas, false); imagesavealpha($canvas, true); } imagefilter($canvas, IMG_FILTER_GRAYSCALE); /* This fully filters PNG's to Grayscale while saving transparency, but for GIF, black background is added to my grayscaled picture, plus, the picture isn't fully grayscale (more like gets high-contrasted with acidic colors). */ // image[png|gif|jpeg] </code></pre> <p><s>What would be the fix, to preserve transparency when applying IMG_FILTER_GRAYSCALE to <code>gif</code>?</s></p> <p>What would be the fix, in order to transform <code>gif</code> to grayscale while saving the transparency? (Question revised due to answer provided by @Pierre)</p> <p>Thanks in advance!</p>

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