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Merge Layer Down doesn't treat opacity correctly


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Or at least not how I think it should treat it. If I have a layer of opacity 255 on top of a layer with opacity 100, and merge down, the result is the top layer, but with opacity 100.

 

The problem is easily recreated. Open a new image; duplicate the background layer; decrease the lower layer's opacity; merge down.

 

I'm using PDN 4.0.9.

 

 

EDIT: I think the correct value for the combined alphas, considered as values between zero and one, should be the sum minus the product.

Edited by MJW
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A workaround is to add a blank layer below your "100" opacity layer, then merge down your 100 layer into blank layer.

That's not a "workaround", it's he proper way to do it. Honestly, that's the only way to calculate the results correctly.

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This is normal.

This happens because you merge 255 layer to 100, not 100 to 255. 255 layer gets opacity 100.

At first I also thought that it is enormous.

If you have another layers about these two, try at first merge 100 layer with above which 255, and then merge 255 layer with result.

 

Sorry for my English :)

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I do think that's the explanation. I've always assumed, without really analyzing it, that the purpose of Merge Layer Down is to produce a layer whose effect is the same as combined effect of the merged layers. After more thought, I realize that's not even generally possible, though it could be done for two Normal blending-mode layers. Although I think that would be a useful way to merge Normal layers, it apparently isn't what Merge Layer Down does, and may be inconsistent with what makes sense for other blend modes.

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