Bug #73291 [Opn]: imagecropauto() $threshold differs from external libgd

Edit report at https://bugs.php.net/bug.php?id=73291&edit=1 ID: 73291 Updated by: cmb@php.net Reported by: cmb@php.net Summary: imagecropauto() $threshold differs from external libgd Status: Open Type: Bug Package: GD related Operating System: * PHP Version: 7.0.11 Block user comment: N Private report: N New Comment: FTR: I've filed a suggestion to improve the algorithm, see <https://github.com/libgd/libgd/issues/334>. Previous Comments: ------------------------------------------------------------------------ [2016-10-11 14:53:04] cmb@php.net Description: ------------ Depending on whether GD is built with the bundled or an external libgd, imagecropauto()'s $threshold argument is treated differently. External libgd assumes mostly much larger $threshold values to crop the same amount from the image than the bundled libgd. The different behavior stems from the different algorithms[1][2]. Actually, I think the algorithm in the bundled is slightly saner than the one in external libgd (but both appear to be somewhat arbitrary). Nonetheless the bundled libgd should be fixed to match the external libgd; otherwise portable code would have to cater to these differences. [1] <https://github.com/libgd/libgd/blob/gd-2.2.3/src/gd_color.c#L14-L16> [2] <https://github.com/php/php-src/blob/PHP-7.0.12/ext/gd/libgd/gd_crop.c#L350-L352> Test script: --------------- <?php $src = imagecreatetruecolor(255, 255); $white = imagecolorallocate($src, 255, 255, 255); imagefilledrectangle($src, 0, 0, 254, 254, $white); for ($i = 254; $i > 0; $i--) { $color = imagecolorallocate($src, $i, $i, $i); imagefilledellipse($src, 127, 127, $i, $i, $color); } foreach ([0.1, 0.5, 1.0, 10.0] as $threshold) { $dst = imagecropauto($src, IMG_CROP_THRESHOLD, $threshold, $white); if ($dst !== false) { printf("size: %d*%d\n", imagesx($dst), imagesy($dst)); } else { printf("cropped to zero size\n"); } } Expected result: ---------------- [external libgd] size: 247*247 size: 237*237 size: 229*229 size: 175*175 Actual result: -------------- [bundled libgd] size: 253*253 size: 219*219 size: 109*109 cropped to zero size ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=73291&edit=1