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.

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.

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();

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

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);

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.