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Bug #66348 setBackgroundColor() has no effect
Submitted: 2013-12-25 08:50 UTC Modified: 2013-12-25 09:57 UTC
From: f21 dot groups at gmail dot com Assigned:
Status: Not a bug Package: imagick (PECL)
PHP Version: 5.5.7 OS: Ubuntu 13.10 64-bit
Private report: No CVE-ID: None
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 [2013-12-25 08:50 UTC] f21 dot groups at gmail dot com 
Description:
------------
setBackgroundColor() does not have any effect.
Imagemagick is compiled from source and the version is ImageMagick 6.8.7-10 Q8 x86_64.

Test script:
---------------
$canvas = new \Imagick();
$canvas->newImage( 50, 50, 'blue');
$canvas->setBackgroundColor('red');
$canvas->writeImage('test.png');

Expected result:
----------------
The image should be red.

Actual result:
--------------
Created image is blue.

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 [2013-12-25 09:15 UTC] mkoppanen@php.net
-Status: Open +Status: Not a bug
 [2013-12-25 09:15 UTC] mkoppanen@php.net 
I am not sure if I agree with the expected result. When you call newImage you create a new image where every pixel is blue.

setBackgroundColor is used for example when reading in formats that don't have background color. Also not that "set<something>" affects all subsequent operations where as "setImage<something>" affects the current image pointer.
 [2013-12-25 09:41 UTC] f21 dot groups at gmail dot com 
Good point!

The problem is that I am trying to work around a bug in imagemagick's coalesce for resizing GIF animations where coalesce will introduce some random background colors.

The workaround is to set -background none when coalescing:
convert animation.gif -background none -coalesce temporary.gif

The problem is that there seems to be no way to set the background to none when running coalesce:

$original = new \Imagick();
$original->readImage($image);
$original = $original->coalesceImages();
$original->setBackgroundColor('none'); //Did not work
$original->setImageBackgroundColor('none'); //Did not work either.
 [2013-12-25 09:43 UTC] mkoppanen@php.net 
As mentioned, setBackgroundColor will affect _subsequent_ operations. Hence the code should probably be:

$original = new \Imagick();
$original->setBackgroundColor('none');
$original->readImage($image);
$original = $original->coalesceImages();
 [2013-12-25 09:49 UTC] f21 dot groups at gmail dot com 
That was also something I tried.

Unfortunately, the setBackgroundColor() did not seem to have any effect.

Here is the gif if you are interested: http://i.stack.imgur.com/6m3RI.gif
 [2013-12-25 09:57 UTC] mkoppanen@php.net 
Does the following solve the issue:


$original = new \Imagick();
$original->readImage('test.gif');

foreach ($original as $frame) {
    $frame->thumbnailImage (160, null);
    $frame->setImageBackgroundColor('none');
}

$original = $original->coalesceImages();
$original->writeImages ('test2.gif', true);
 [2013-12-25 10:03 UTC] f21 dot groups at gmail dot com 
Perfect! That appears to have solved the problem!

Would love to see some more documentation for setImageBackgroundColor() and setBackgroundColor() as they are a bit sparse at the moment.

Would love to have a way to do this without having to loop through all the frames though.
 
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