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

ID: 41820 Updated by: pajoye@php.net Reported By: richard dot gavenda at rksting dot cz Status: Open Bug Type: GD related Operating System: Windows XP PHP Version: 5.2.3 Assigned To: pajoye New Comment: It is what I said, a rounding issue. I'm not sure yet how to make it more portable. Previous Comments: ------------------------------------------------------------------------ [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? ------------------------------------------------------------------------ [2007-06-27 10:08:39] richard dot gavenda at rksting dot cz Title correction ------------------------------------------------------------------------ [2007-06-27 10:07:40] richard dot gavenda at rksting dot cz Description: ------------ When resizing an image filled with solid color using imagecopyresampled, a destination image is not filled with same solid color, but with noise of two colors. I was tried this with grayscale images. Second color in noise was exactly same as source color, but with RGB channels lowered by 1. When the source image was filled with color, which had RGB channels values equal to power of 2 (0,1,2,4,8,16,32,64,128) the noise disappears. Reproduce code: --------------- $im = imagecreatetruecolor(1045,600); $back = imagecolorallocate($im, 100, 100, 100); imagefill($im, 0, 0, $back); $im2 = imagecreatetruecolor(383,220); imagecopyresampled($im2,$im,0,0,0,0,383,220,1045,600); imagepng($im2); Expected result: ---------------- PNG file filled with color 100,100,100(RGB) Actual result: -------------- PNG file filled with color noise of 100,100,100(RGB) and 99,99,99(RGB) ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=41820&edit=1