ID: 23815 Comment by: andre at webkr dot de Reported By: bjorn at smokingmedia dot com Status: Assigned Bug Type: Feature/Change Request Operating System: Linux pluto 2.4.18lvm-r1 PHP Version: 5.2.9 Assigned To: pajoye New Comment:
So what does the "it implements alpha transparency for true colour images" in "When pct = 0, no action is taken, when 100 this function behaves identically to imagecopy() for pallete images, while it implements alpha transparency for true colour images." mean anyway? Previous Comments: ------------------------------------------------------------------------ [2009-07-20 12:10:43] steve at redmonkey dot org Thanks, understood. Although, I do think it would be a useful feature, perhaps there's scope for an 'imagecopymergealpha' type function in the future? ------------------------------------------------------------------------ [2009-07-20 08:43:04] paj...@php.net imagecopymerge was not meant to support the alpha channel but to emulate it via pct. It was also not meant to use both the alpha or the pct value to blend an image over another. ------------------------------------------------------------------------ [2009-07-20 05:44:49] steve at redmonkey dot org To make life a little easier I've put the notes and examples together on a simple web page at http://www.redmonkey.org/php-bug-23815/ After investigating the code base a little further I've realised my patch solution can be made more efficient as there is no need to make a copy of the source or pass the image over to gdImageCopy once the new alpha level has been set as we've already done the all the work and can simply set the pixels RGBA index within the second image scan. The revised patch (which is also available from a link on the web page) 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 2009-07-20 05:54:21.709936176 +0100 @@ -2255,6 +2255,67 @@ 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. + */ + int ca, cr, cg, cb; + float na; + float ac; + + /* 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 (src, srcX + x, srcY + y); + ca = gdImageAlpha(src, 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 (src, srcX + x, srcY + y); + ca = gdImageAlpha(src, c); + cr = gdImageRed(src, c); + cg = gdImageGreen(src, c); + cb = gdImageBlue(src, c); + + na = (ca + gdAlphaMax - (gdAlphaMax * ((float)pct / 100))) * ac; + na = (na > gdAlphaMax)? gdAlphaMax : ((na < gdAlphaOpaque)? gdAlphaOpaque: na); + + int nc = gdImageColorAllocateAlpha(src, cr, cg, cb, (int)na); + if (nc == -1) { + gdImageColorClosestAlpha(src, cr, cg, cb, (int)na); + } + + gdImageSetPixel (dst, dstX + x, dstY + y, nc); + } + } + + return; + } + for (y = srcY; y < (srcY + h); y++) { tox = dstX; for (x = srcX; x < (srcX + w); x++) { ------------------------------------------------------------------------ [2009-07-20 01:52:43] steve dot denim at redmonkey dot org I 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++) { ------------------------------------------------------------------------ [2009-05-04 12:14:15] checat at yandex dot ru Please try again: site with images is up and running. I've also uploaded files to alternate location, get them from http://checat.narod.ru/php-bug-23815/ ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at http://bugs.php.net/23815 -- Edit this bug report at http://bugs.php.net/?id=23815&edit=1
