Bug #75124 [Ana->Csd]: gdImageGrayScale() may produce colors

From: Date: Sun, 27 Aug 2017 12:20:32 +0000
Subject: Bug #75124 [Ana->Csd]: gdImageGrayScale() may produce colors
References: 1  Groups: php.bugs 
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Edit report at https://bugs.php.net/bug.php?id=75124&edit=1

 ID:                 75124
 Updated by:         cmb@php.net
 Reported by:        cmb@php.net
 Summary:            gdImageGrayScale() may produce colors
-Status:             Analyzed
+Status:             Closed
 Type:               Bug
 Package:            GD related
 Operating System:   *
 PHP Version:        7.0.22
 Assigned To:        cmb
 Block user comment: N
 Private report:     N

 New Comment:

Automatic comment on behalf of cmbecker69@gmx.de
Revision: http://git.php.net/?p=php-src.git;a=commit;h=499f5480f1a9b3063097b53592c37329c1d5f6f8
Log: Fixed bug #75124 (gdImageGrayScale() may produce colors)


Previous Comments:
------------------------------------------------------------------------
[2017-08-27 11:32:57] cmb@php.net

Description:
------------
For ease of reference, I'm forwarding libgd bug #386[1].

TL;DR: gdImageGrayScale() misses to switch to gdEffectReplace
alpha blending mode before calling gdImageSetPixel which may
result in colored images.

[1] <https://github.com/libgd/libgd/issues/386>

Test script:
---------------
<?php

$im = imagecreatefrompng(__DIR__ . '/wings.png');
imagefilter($im, IMG_FILTER_GRAYSCALE);
imagepng($im, __DIR__ . '/wings-out.png');


Expected result:
----------------
The generated wings-out.png should be a pure grayscale image.

Actual result:
--------------
The generated wings-out.png shows faintly purple colors.


------------------------------------------------------------------------



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Edit this bug report at https://bugs.php.net/bug.php?id=75124&edit=1

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