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[2003-05-26 11:43 UTC] bjorn at smokingmedia dot com
[[There are similar bugs in the system, but they are either closed or said to be fixed... i think it's still not fixed..]] i wanted to do the following. Use a transparent PNG-24(24 bits) file, with an alpha-channel (with a drop-shadow) and merge it to a background color. (see sample code). this works: imagecopy($backgroundimage, $image_id, 0, 0, 0, 0, $im_X, $im_Y); this doesn't work: imagecopymerge($backgroundimage, $image_id, 0, 0, 0, 0, $im_X, $im_Y, 99); -> with any number instead of 99 sample link: [change the hex color code to change backgroundcolor] this is Okay http://www.smokingmedia.com/test_gd_fb/test?bg=ffee22 this is not okay: http://www.smokingmedia.com/test_gd_fb/test_nk?bg=ffee22 sample code: <?php if(!isset($_GET[bg]) || $_GET[bg] == ""){ $bg = "eeeeee"; } else{ $bg = $_GET[bg]; } $im = "test01.png"; // // function to convert hex colorcode to decimal // function colordecode($hex){ $code[r] = hexdec(substr($hex, 0 ,2)); $code[g] = hexdec(substr($hex, 2 ,2)); $code[b] = hexdec(substr($hex, 4 ,2)); return $code; } // end func colordecode // create the resource id $image_id = imageCreateFromPNG($im); // get image size $im_X = ImageSX($image_id); $im_Y = ImageSY($image_id); // create a truecolor background image of the right size $backgroundimage = imagecreatetruecolor($im_X, $im_Y); // get the desired backgroundcolor: $code = colordecode($bg); $backgroundcolor = ImageColorAllocate($backgroundimage, $code[r], $code[g], $code[b]); ImageFilledRectangle($backgroundimage, 0, 0, $im_X, $im_Y, $backgroundcolor); // merge the two together with alphablending on! ImageAlphaBlending($backgroundimage, true); // this works: imagecopy($backgroundimage, $image_id, 0, 0, 0, 0, $im_X, $im_Y); // this is where things go wrong: //imagecopymerge($backgroundimage, $image_id, 0, 0, 0, 0, $im_X, $im_Y, 99); // output the image: Header( "Content-type: image/png"); ImagePNG($backgroundimage); // destroy the memory ImageDestroy($backgroundimage); ImageDestroy($image_id); ?> PatchesPull Requests
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Last updated: Sat Nov 01 14:00:01 2025 UTC |
PHP version: 5.2.9 CentOS 4 Reproduce code: <?php $bg = imagecreatefrompng('http://guppi.spb.ru/php-bug-23815/bg.png'); $over = imagecreatefrompng('http://guppi.spb.ru/php-bug-23815/over.png'); imagecopymerge($bg, $over, 0,0,0,0,32,32,100); imagecopymerge($bg, $over, 16,0,0,0,32,32,50); imagepng($bg, 'imagecopymerge.png'); ?> Expected result: Proper image: http://guppi.spb.ru/php-bug-23815/proper.png Actual result: Wrong image: http://guppi.spb.ru/php-bug-23815/imagecopymerge.pngI have run into the same problem and can reproduce the example from checat at yandex dot ru. I have also provided additional examples and a patch for the solution I have come with. For the examples I've used two image files 'tux.png' for the background (destination) image and 'ff-logo-sm.png' for the overlay (source) image, these can be found at www.redmonkey.org/php-bug-23815/tux.png and www.redmonkey.org/php-bug-23815/ff-logo-sm.png respectively. If I run these images through imagecopy() with the following code.. $bg = imagecreatefrompng('tux.png'); $over = imagecreatefrompng('ff-logo-sm.png'); imagealphablending($bg, true); imagesavealpha($bg, true); imagecopy($bg, $over, 276, 300, 0, 0, 123, 119); imagepng($bg, 'tux-fox-imagecopy.png'); The alpha channels of both images seem to be handleed and merged/blended in a way that I think most users would expect, the resulting image can be found at www.redmonkey.org/php-bug-23815/tux-fox-imagecopy.png However, if I run the two images through imagecopymerge with the following code.. $bg = imagecreatefrompng('tux.png'); $over = imagecreatefrompng('ff-logo-sm.png'); imagealphablending($bg, true); imagesavealpha($bg, true); imagecopymerge($bg, $over, 276, 300, 0, 0, 123, 119, 100); imagepng($bg, 'tux-fox-imagecopymerge-100-without-patch.png'); The resulting image is not what I would expect, in this case, it seems that the alpha channel of the destination image is maintained but the alpha channel of the source image is completely ignored, the resulting image can be found at www.redmonkey.org/php-bug-23815/tux-fox-imagecopymerge-100-without-patch.png Applying a 50% reduction in opacity.. $bg = imagecreatefrompng('tux.png'); $over = imagecreatefrompng('ff-logo-sm.png'); imagealphablending($bg, true); imagesavealpha($bg, true); imagecopymerge($bg, $over, 276, 300, 0, 0, 123, 119, 50); imagepng($bg, 'tux-fox-imagecopymerge-50-without-patch.png'); Also has the same issue, the resulting image can be found at www.redmonkey.org/php-bug-23815/tux-fox-imagecopymerge-50-without-patch.png After applying my patch the results from imagcopymerge are more inline with what I persoanlly would expect in that the alpha channels of both images are maintained during the copy/merge process. With the following code.. $bg = imagecreatefrompng('tux.png'); $over = imagecreatefrompng('ff-logo-sm.png'); imagealphablending($bg, true); imagesavealpha($bg, true); imagecopymerge($bg, $over, 276, 300, 0, 0, 123, 119, 100); imagepng($bg, 'tux-fox-imagecopymerge-100-with-patch.png'); The resulting image can be viewed at www.redmonkey.org/php-bug-23815/tux-fox-imagecopymerge-100-with-patch.png And with the following code.. $bg = imagecreatefrompng('tux.png'); $over = imagecreatefrompng('ff-logo-sm.png'); imagealphablending($bg, true); imagesavealpha($bg, true); imagecopymerge($bg, $over, 276, 300, 0, 0, 123, 119, 50); imagepng($bg, 'tux-fox-imagecopymerge-50-with-patch.png'); The resulting image can be viewed at www.redmonkey.org/php-bug-23815/tux-fox-imagecopymerge-50-with-patch.png The patch as applied to ext/gd/libgd/gd.c is as follows..... --- php-5.3.0/ext/gd/libgd/gd.c 2009-05-27 08:17:54.000000000 +0100 +++ php-5.3.0-build/ext/gd/libgd/gd.c 2009-07-19 22:28:37.312702552 +0100 @@ -2255,6 +2255,83 @@ int ncR, ncG, ncB; toy = dstY; + if (pct == 100) { + /* no opacity adjustment required pass through to gdImageCopy() */ + gdImageCopy(dst, src, dstX, dstY, srcX, srcY, w, h); + return; + } + + if (pct == 0) { + /* 0% opacity? nothing needs to be done */ + return; + } + + if (src->trueColor && dst->trueColor) { + /* support for maintaining the alpha (transparency) of both source and + * destination images (assuming they are true colour) while opacity blending. + */ + gdImagePtr srcback; + int ca, cr, cg, cb; + float na; + float ac; + + /* we adjust the alpha levels on a copy of the source image, the copy + * only needs to be as large as the crop area if there is one + */ + srcback = gdImageCreateTrueColor (w, h); + if (srcback==NULL) { + return; + } + + gdImageAlphaBlending(srcback, 0); + gdImageSaveAlpha(srcback, 1); + gdImageCopy(srcback, src, 0, 0, srcX, srcY, w, h); + + /* we need to loop through the src image to get the max transparency level */ + int mt = 0; + + for (y = 0; y < h; y++) { + for (x = 0; x < w; x++) { + c = gdImageGetTrueColorPixel (srcback, x, y); + ca = gdImageAlpha(srcback, c); + + mt = ca > mt ? ca : mt; + } + } + + /* src has no transparency? set to use full alpha range */ + mt = mt == gdAlphaOpaque ? gdAlphaMax : mt; + + /* alpha correction factor */ + ac = (float)mt / gdAlphaMax; + + /* loop through the image again and set/adjust alpha channel level */ + for (y = 0; y < h; y++) { + for (x = 0; x < w; x++) { + c = gdImageGetTrueColorPixel (srcback, x, y); + ca = gdImageAlpha(srcback, c); + cr = gdImageRed(srcback, c); + cg = gdImageGreen(srcback, c); + cb = gdImageBlue(srcback, c); + + na = (ca + gdAlphaMax - (gdAlphaMax * ((float)pct / 100))) * ac; + na = (na > 127.0f)? 127.0f : ((na < 0.0f)? 0.0f: na); + + int nc = gdImageColorAllocateAlpha(srcback, cr, cg, cb, (int)na); + if (nc == -1) { + gdImageColorClosestAlpha(srcback, cr, cg, cb, (int)na); + } + + gdImageSetPixel (srcback, x, y, nc); + } + } + + /* finally dispatch to gdImageCopy to do the actual copying */ + gdImageCopy(dst, srcback, dstX, dstY, 0, 0, w, h); + gdImageDestroy(srcback); + return; + } + for (y = srcY; y < (srcY + h); y++) { tox = dstX; for (x = srcX; x < (srcX + w); x++) {IMHO, imagecopymerge() should finally be removed in the long run. Its purpose is to emulate alpha, what was necessary before GD introduced truecolor images with proper alpha channels. Therefore, I'm against adding further alpha support to imagecopymerge() or even an additional function. Instead, imagefilter() could be used to either increase the alpha values or to decrease the color values. IMG_FILTER_COLORIZE already allows this, but one can't specify a percentage, so can't get the exact same effect. The following example shows that one could already come a long way, though: <?php $bg = imagecreatefrompng(__DIR__ . '/23815-bg.png'); $over = imagecreatefrompng(__DIR__ . '/23815-over.png'); imagecopy($bg, $over, 0, 0, 0, 0, 16, 32); imagealphablending($over, false); imagefilter($over, IMG_FILTER_COLORIZE, 0, 0, 0, +32); imagecopy($bg, $over, 16, 0, 0, 0, 16, 32); imagepng($bg, __DIR__ . '/23815-out.png'); Anyhow, this is a general libgd issue (not particularly related to PHP's bundled libgd), so I have filed <https://github.com/libgd/libgd/issues/370> and suspend this feature request.