#39273 [Bgs]: imagecopyresized() not compatable with alpha channel

ID: 39273 User updated by: seth at pricepages dot org Reported By: seth at pricepages dot org Status: Bogus Bug Type: GD related Operating System: Mac 10.4 PHP Version: 5.1.6 Assigned To: pajoye New Comment: But that has one of the bugs that I pointed out: boolean transparency. The original doesn't have that problem. Previous Comments: ------------------------------------------------------------------------ [2006-10-28 14:04:59] pajoye@php.net Use the code I just gave you, it does create the resized version (by copying): http://blog.thepimp.net/misc/39273_out.png ------------------------------------------------------------------------ [2006-10-28 13:15:45] seth at pricepages dot org I ran your code before I posted my last comment, but I still don't know what you are implying. The results are exactly as I expect them to be. If this bug is bogus, please tell me how I can create an enlarged version of test.png? It isn't possible without applying a fix. ------------------------------------------------------------------------ [2006-10-28 10:49:54] pajoye@php.net "I am aware that the image is fully black, except for variations in alpha. That is why this is a bug related to the alpha channel and not any other." You are not aware that your image is *NOT* fully black. Background color (the transparent color) is not the same than a color with a ALPHA component. Please run the code I gave you, read the results (like the values of the channels in these two pixels, or any other). ------------------------------------------------------------------------ [2006-10-27 17:22:07] seth at pricepages dot org I am aware that the image is fully black, except for variations in alpha. That is why this is a bug related to the alpha channel and not any other. Well, I went in and fixed it myself. The problem was in the function gdImageGetTrueColorPixel(). It assumed that palette images always have binary transparency, with a correct value in im->transparent. Because my source image didn't have a correct value in im->transparent, it was always marked as opaque. This line: return gdTrueColorAlpha(im->red[p], im->green[p], im->blue [p], (im->transparent == p) ? gdAlphaTransparent : gdAlphaOpaque); Needs to be changed to: return gdTrueColorAlpha(im->red[p], im->green[p], im->blue [p], (im->transparent == p) ? gdAlphaTransparent : im->alpha [p]); Making this patch also fixes the same bug in imagecopyresampled(), and who knows what else. Although, I would recommend using gdTrueColorAlpha() at the appropriate point(s) in gdImageCopyResized() instead of gdImageGetTrueColorPixel(). This would eliminate an extra function call, branch, and color lookup. ------------------------------------------------------------------------ [2006-10-27 14:01:12] pajoye@php.net There is nothing wrong in imagecopyresize (or imagecopy). The problem you have is the misunderstanding of what is the background color, the alpha channel and alpha blending. Your original image has many black colors, one is transparent (what you consider as background), and the other with various transparency levels. Try the code below, it will explain you what is your image and how it works. <?php $small = imagecreatefrompng('39273.png'); print_r(imagecolortransparent($small)); $width = 300; $height = 300; $srcW = imagesx($small); $srcH = imagesy($small); print_r(imagecolorsforindex($small, imagecolorat($small, 0,0))); // one of the ""black"" pixel print_r(imagecolorsforindex($small, imagecolorat($small, 37,1))); imagecolortransparent($small, 1); $img = imagecreatetruecolor($width, $height); $trans = imagecolorresolve($img,255,255,255); imagefill($img, 0,0, $trans); imagecolortransparent($img, $trans); imagecopyresized($img, $small, 0,0, 0,0, $width, $height, $srcW, $srcH); imagepng($img, '1.png'); ------------------------------------------------------------------------ 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/39273 -- Edit this bug report at http://bugs.php.net/?id=39273&edit=1