Question

Let’s say we have layer0 with opacity 100%, and layer1 with opacity 50%, layer1 merged down with layer0 as new file.
Now we have this new file and the original layer0, any chance to work out the original layer1?

Thanks for any help.

Answer 1

The fact that layer0 has 100% opacity, is not that meaningful (if it’s less than 100%, what should we see through it?). An opacity of 70% usually means, we see the the weighted average of this layer for 70% and the layer beneath it for 30%.

For every pixel new expressed in pixels from layer0 and layer1:

new = layer0*(1-0.5) + layer1*0.5

rearranging terms:

layer1 = 2*(new - layer0*(1-0.5))

Because of possible rounding (pixels are usually stored in range of 0-255), you might not get the exact original layer back. Every pixel could be off by 1.