Fix PNG images being loaded without premultiplying its alpha channels #682
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Yttruire
commented
May 25, 2023
guusw
requested changes
May 29, 2023
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Also, you need to move the premultiple/unpremultiply template functions to a header (can add imaging.hpp) if you want to use them in serialization.cpp |
sinkingsugar
approved these changes
Jun 5, 2023
Codecov Report
@@ Coverage Diff @@
## devel #682 +/- ##
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+ Coverage 80.56% 80.62% +0.06%
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Files 257 258 +1
Lines 33046 33135 +89
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+ Hits 26623 26716 +93
+ Misses 6423 6419 -4
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CI should be fixed now, seems to have been an issue with visibility of the implemented functions within the header file |
src/core/shards/imaging.cpp
Outdated
| @@ -313,10 +397,10 @@ struct Resize { | |||
| void registerShards() { | |||
| REGISTER_SHARD("Convolve", Convolve); | |||
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Wonder if it's time to introduce a Image prefix and change those into like Image.Resize?
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@Yttruire Can you add some add a test case for PremultiplyAlpha & DemultiplyAlpha in the image script (or a new script) |
To be refactored because it currently opens the file twice in order to verify its type
Problem is related to the templates and name resolution in imaging.hpp with the new premultiplyAlpha and demultiplyAlpha template functions
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…eter to LoadImage. Also refactor premultiplying alpha in serialization
…com/fragcolor-xyz/shards into zh/fix-premultiplied-alpha-channels
…/github.com/fragcolor-xyz/shards into zh/fix-premultiplied-alpha-channels" This reverts commit 510e3a5, reversing changes made to 697d170.
…emultiplyAlpha divide by 0
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PNG images are guaranteed by the file standards to not contain premultiplied alpha channels, and use straight alpha channels. As a result, PNGs will be rendered wrongly as the un-premultiplied alpha channels are used to render the image.
This PR fixes
LoadImage. It will now check if the loaded image is a PNG and if so, premultiplies the alpha channels, then flags the image as having a premultiplied alpha channel. If images that are not PNG, it will assume that they are already premultiplied and simply flag them as premultiplied. This PR also adds two shards PremultiplyAlpha and DemultiplyAlpha for manually premultiplying the alpha and demultiplying alpha of an image.Some refactoring is also done for the premultiplying and demultiplying of the alpha channels.
LoadImage's code for loading byte inputs and files have also been streamlined in the process.Note: Checking image file type for PNG can be done according to the specifications @ http://www.libpng.org/pub/png/spec/1.2/PNG-Structure.html
Additional list of file signatures: https://en.wikipedia.org/wiki/List_of_file_signatures
Fixes #671