psd: Fix alpha blending (KF5)

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PSD files are saved with as alpha premultiplied. The problem is that alpha refers to white instead of black so it requires transformation formulas. Then, to conver PS premultiplied to QImage premultiplied you have to use the following formula:

* V = Alpha + Vps - Max (C, M, Y, K, R, G, B, Gray, L\* components)
* V = Vps + (Alpha - Max + 1) / 2 (a\*, b\* components)

Where Max is the maximum value depending on the image depth and Vps is the valued read from the file.

This is a port of MR !143 to KF5.

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This commit is contained in:

Mirco Miranda

2023-03-29 17:58:09 +00:00

committed by Albert Astals Cid

parent 64f3303ef0

commit e96b43aef5

6 changed files with 105 additions and 22 deletions

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