ID: 45030 Updated by: [EMAIL PROTECTED] Reported By: lieyang at yahoo dot com -Status: Open +Status: Feedback Bug Type: GD related Operating System: x86_64 GNU/Linux Kernel 2.6.9-4 PHP Version: 5.2.6 Assigned To: pajoye New Comment:
Right, there is a alpha values between 0 and 2. This is a little rounding issue in the interpolation function. As it is not relevant when you use the full range of the 8bit (7bit in gd 2.0.x internals), it could cause some troubles when you introduce more errors while using only 4bits. The worst case will end with an error twice bigger than the original one. That's certainly why you see the little black pixels. Here is an attempt to minimize the error in the edge of the alpha values: http://pierre.libgd.org/patches/bug45030.txt It should fix non obvious errors like the one you had. Previous Comments: ------------------------------------------------------------------------ [2008-05-18 16:14:25] lieyang at yahoo dot com You can see the noise on both my 56x56 image and image generated from Rasmus's reproducing code sample with resizing from 90x90 to 50x50 (I am not talking about the anti-aliasing areas :) GIMP: Tools > Selection Tools > By Color select, click a few spots in the empty region of the image and you will see the noise being selected. Paint.net: use the color select tool and click a few times on the empty region of the image, some pixels will display the transparency as 2. (thank you so much for your quick response!) ------------------------------------------------------------------------ [2008-05-18 10:29:14] [EMAIL PROTECTED] The 56x56 image looks perfectly fine to me. I also checked the alpha values for the translucent areas and they look fine too (full translucent when they are not near the star anti aliased pixels, as expected). To see how is the alpha channel in the result image, please look at this zoomed version of the alpha channel only: http://pierre.libgd.org/bugs/45030_alpha_only.png 100% black means opaque and the gray squares are only to show a background (what would be behind the image). As you can see, there is no noise in the transparent areas. Are you sure that there is not a bug in the Motorola display system? Maybe it does not support semi transparent pixels. ------------------------------------------------------------------------ [2008-05-18 03:51:39] lieyang at yahoo dot com Here are my test source image (png 90x90): http://tinyurl.com/65tdtm Resized to 56x56 with noise in alpha channel: http://tinyurl.com/6yold7 ------------------------------------------------------------------------ [2008-05-18 03:41:50] lieyang at yahoo dot com Please try the following with different image sizes and you will see that the alpha channel has noise. (I have two original before and after images but can not find the link to upload them as attachments) $imageSrc = imagecreatetruecolor(90, 90); imagealphablending($imageSrc, false); imagesavealpha($imageSrc, true); $color = imagecolorallocatealpha($imageSrc, 0, 0, 0, 127); imagefill($imageSrc, 0, 0, $color); $imageDst = imagecreatetruecolor(56, 56); imagealphablending($imageDst, false); imagesavealpha($imageDst, true); imagecopyresampled($imageDst,$imageSrc, 0, 0, 0, 0, 56, 56, 90, 90); header('Content-type: image/png'); imagepng($imageDst); ------------------------------------------------------------------------ [2008-05-17 23:11:41] [EMAIL PROTECTED] We need a better reproducible example here, including the source image. When the source image has a perfect alpha channel, I see no noise. Try this: $imageSrc = imagecreatetruecolor(500, 500); imagealphablending($imageSrc, false); imagesavealpha($imageSrc, true); $color = imagecolorallocatealpha($imageSrc, 0, 0, 0, 127); imagefill($imageSrc, 0, 0, $color); $imageDst = imagecreatetruecolor(50, 50); imagealphablending($imageDst, false); imagesavealpha($imageDst, true); imagecopyresampled($imageDst,$imageSrc, 0, 0, 0, 0, 50, 50, 500, 500); header('Content-type: image/png'); imagepng($imageDst); ------------------------------------------------------------------------ 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/45030 -- Edit this bug report at http://bugs.php.net/?id=45030&edit=1