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Add an option to decode to a premultiplied form #271
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If you want premultiplied alpha, isn't the right approach to apply it yourself before saving the PNG? |
No, PNGs are stored using unpremultiplied alpha. Premultiplying before saving will cause other png decoders to apply the alpha twice and won't help with existing images. |
I've clarified the title to make it clearer that this would probably be an optional output transformation. |
There are at least two case where applying the transformation at decode time, instead of later, is advantageous compared to a post-processing step after the full buffer is decoded. There is no general benefit however, so their implementation mustn't have too much of a complexity overhead.
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Applying at decode time can also avoid cache thrashing on large images. |
Sorry for the noob question: If |
Consumers of PNG images often want the alpha premultiplied. See jrmuizel/raqote#167
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