Preserve alpha channel in Imagick negative effect#877
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Thanks for merging this so fast @mlocati! |
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effects()->negative()on the Imagick driver inverts the alpha channel as well as the colours, which GD doesn't do. Result: an opaque image comes back fully transparent. The colour values are right, you just can't see them.Cause is
negateImage(false, \Imagick::CHANNEL_ALL).CHANNEL_ALLincludes alpha, so opaque alpha flips to transparent. GD avoids this becauseIMG_FILTER_NEGATEonly touches colour.Fix is to negate with
CHANNEL_ALL & ~CHANNEL_ALPHAso only the colour channels flip (same thing intervention/image does). The Gmagick driver doesn't need it: in the gd-gmagick docker imageCHANNEL_ALLleaves an opaque image opaque, and Gmagick's CHANNEL constants are sequential enum values rather than bitmasks, so the& ~trick wouldn't apply anyway.Added
testNegatePreservesAlphatoAbstractEffectsTestso every driver gets covered. It negates a fully-opaque image and asserts it stays opaque. Fails on Imagick before the fix (alpha 100 to 0), passes after. Verified the full suite green in both the gd-imagick and gd-gmagick docker images.