#41820 [Ana->Opn]: Color noise in resized image when using IMAGECOPYRESAMPLED

ID: 41820 User updated by: richard dot gavenda at rksting dot cz Reported By: richard dot gavenda at rksting dot cz -Status: Analyzed +Status: Open Bug Type: GD related Operating System: Windows XP PHP Version: 5.2.3 Assigned To: pajoye New Comment: So there must be some sort of bug in resampling algorithm. When i resizing bitmap filled with solid color in any bitmap editor, using any aproximation (linear, bicubic, etc.) I get an image filled with exactly same solid color. With this issue I'm unable to reach one bit transparency of resized image. Previous Comments: ------------------------------------------------------------------------ [2007-06-28 10:08:08] pajoye@php.net "Position of horizontal and vertical stripes is different on different machines." Yes, it is the problem with floating points value when we need a constant and precise result on different architecture. See; http://docs.sun.com/source/806-3568/ncg_goldberg.html for a good explanation about this problem. For example, your images has variation between 126 and 127 for a given channel. It may be only something like 126.49999 and 126.50000. I don't think I can fix it easily for this implementation (bicubic interpolation using floating points implementation). Future versions will have more filters and using less volatile precisions. ------------------------------------------------------------------------ [2007-06-28 10:00:33] richard dot gavenda at rksting dot cz Position of horizontal and vertical stripes is different on different machines. ------------------------------------------------------------------------ [2007-06-28 09:58:20] pajoye@php.net It is what I said, a rounding issue. I'm not sure yet how to make it more portable. ------------------------------------------------------------------------ [2007-06-28 09:53:41] richard dot gavenda at rksting dot cz AMD 32, Windows XP, PHP 5.2.3 - bug present x86 64, Centos 4, PHP 4.3.9 - bug present x86 32, Fedora Core 5, PHP 5.1.6 - bug present Source image 800x600 filled with RBG(127,127,127): target image 800x600 - OK http://81.200.49.53:25459/resample.php?w=800&h=600&c=127 target image 701x600 - vertical stripes http://81.200.49.53:25459/resample.php?w=701&h=600&c=127 target image 800x501 - horizontal stripes http://81.200.49.53:25459/resample.php?w=800&h=501&c=127 target image 701x501 - noise http://81.200.49.53:25459/resample.php?w=701&h=501&c=127 "When is source image filled with RGB values equal to power of 2 (0,1,2,4,8,16,32,64,128) the noise disappears", this rule i can reproduce only on AMD 32 architecture. On other platform is noise present regardless of fill color. ------------------------------------------------------------------------ [2007-06-28 07:29:29] pajoye@php.net CopyResampled using floating points to calculate the destination color. It may result to rounding problem. However I cannot reproduce this problem on my development platforms (x86 32 and 64bit, amd 64). What's your architecture? ------------------------------------------------------------------------ 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/41820 -- Edit this bug report at http://bugs.php.net/?id=41820&edit=1