Bug #67325 [Opn->Ana]: imagetruecolortopalette: many colors in palette are missing

Edit report at https://bugs.php.net/bug.php?id=67325&edit=1 ID: 67325 Updated by: cmb@php.net Reported by: icp at freigre dot com Summary: imagetruecolortopalette: many colors in palette are missing -Status: Open +Status: Analyzed Type: Bug Package: GD related PHP Version: 5.5.12 -Assigned To: +Assigned To: cmb Block user comment: N Private report: N New Comment: I can confirm the issue. The culprit has already been hinted at in bug #28949, namely the change to cater to total==0[1]. Just from looking at the code, the condition in the following line is obviously wrong; we don't want to test count but rather total to avoid the division by zero. After fixing this, some quick tests confirm that there are no more duplicate palette colors. As this issue also affects libgd, I'm going to fix it there first, and will port the fix to PHP's bundled libgd. > have you tried using the new algo? Afair it is not exposed in > php but it provides a way better quality in that regard. Actually, gdImageTrueColorToPaletteSetMethod() and gdImageTrueColorToPaletteSetQuality() are not yet available in PHP's bundled libgd. Seems it doesn't get boring. :-) [1] <https://github.com/php/php-src/blob/PHP-7.0.11/ext/gd/libgd/gd_topal.c#L762-L774> <https://github.com/libgd/libgd/blob/gd-2.2.3/src/gd_topal.c#L661-L670> Previous Comments: ------------------------------------------------------------------------ [2014-11-10 14:02:37] pajoye@php.net Given that the default algo works with similar colors to create palettes, it sounds like we may not be able to fix it. @remi have you tried using the new algo? Afair it is not exposed in php but it provides a way better quality in that regard. ------------------------------------------------------------------------ [2014-11-08 07:42:29] remi@php.net I can reproduce, with php 5.4.34 (bundled libgd) and 5.6.3RC1 (system libgd) Result (with or without dither) have 187 different colors, 70 are white. ------------------------------------------------------------------------ [2014-05-22 11:42:22] icp at freigre dot com Description: ------------ This bug has been already posted 2004 here: https://bugs.php.net/bug.php?id=28949 But the bug is still alive in PHP 5.5! I convert a truecolor image with 1000s of different colors into a palette image using imagetruecolortopalette ($image, no, 256) But the palette of the resulting image doesn't contain the 256 most appearing individual colors of the original truecolor image. Many of the palette colors are just white (RGB value: #FF FF FF). For example just 120 colors are individual, the rest of 136 palette entries is white. This results in a worse color reproduction of the palette image than it should be using 256 individual colors. Please fix this bug, since imagetruecolortopalette is very important for creating small-filesized GIF and PNG images. Their filesize is dramatically lower than its truecolor counterpart while retaining satisfying output quality. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=67325&edit=1