Bug #75072 [Opn->Nab]: imagepng does not produce lossless output when input is lossy

Edit report at https://bugs.php.net/bug.php?id=75072&edit=1 ID: 75072 Updated by: cmb@php.net Reported by: choinnn1 at gmail dot com Summary: imagepng does not produce lossless output when input is lossy -Status: Open +Status: Not a bug Type: Bug Package: GD related Operating System: Windows 8.1 PHP Version: 7.1.8 -Assigned To: +Assigned To: cmb Block user comment: N Private report: N New Comment: > php-logo_php.png should be visually 100% identical to both > php-logo.jpeg and php-logo_paint.png. This assumption is not in agreement with the JPEG standard, which does not require all decoders to produce identical output images. See also <https://stackoverflow.com/questions/23565889/jpeg-images-have-different-pixel-values-across-multiple-devices#23714501>. Previous Comments: ------------------------------------------------------------------------ [2017-08-13 19:01:08] choinnn1 at gmail dot com Description: ------------ 1. Save image: http://www.softaculous.com/blog/wp-content/uploads/2013/04/php-logo.jpeg as php-logo.jpeg 2. Open php-logo.jpeg in Windows Paint, save as php-logo_paint.png 3. Write a script in PHP to convert php-logo.jpeg into php-logo_php.png Test script: --------------- imagepng(imagecreatefromjpeg('C:\php-logo.jpg'), 'C:\php-logo_php.png'); Expected result: ---------------- php-logo_php.png should be visually 100% identical to both php-logo.jpeg and php-logo_paint.png. Actual result: -------------- php-logo_php.png contains slightly different colors when compared to php-logo.jpeg and php-logo_paint.png. See the diff (made with Beyond Compare): php-logo.jpeg vs php-logo_php.png: http://i.imgur.com/0nY42bF.png php-logo.jpeg vs php-logo_paint.png: http://i.imgur.com/sjgyHAE.png Note: php-logo_paint.png is 32-bit PNG image by default for me, but it's not relevant. If I convert it to 24-bit PNG or use Paint.NET instead of Microsoft Paint from the start, the result will be the same. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=75072&edit=1