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RobinMcL

Create a layer from the difference between two other layers

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I want to make a new layer  which is the content of one layer minus the shared content of another layer.

In other words, I want to isolate the difference between two layers.

I have used a stack to remove this difference (as in the tutorial) but I don't want this discarded. I want it as a new layer.

The problem comes from a physical collage that is being made in, essentially, four physical layers. I want to have a digital counterpart and I thought about doing it the following way.

Make layer 1. Photograph it. Add layer 2, Photograph it. In Affinity Photo have these two photos as layers. Subtract, from image 2, what it shares with image 1 and save as a new layer. Continue in this way till the collage is finished. I now have a photo of the final collage BUT if I do need to edit this, I have isolated the separate entities and that will make the editing so much easier. I could do this by selecting pieces from the final image but this can be very tricky. It would be so much easier if I could do this as the collage is being made.

In short, it's like the removal using a stack with the additional capability of "remove to a new layer".

I'd be happy to have suggestions.

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Would Merge Visible applied to the two visible layers with a Difference blending mode do what you want?

John


Windows 10, Affinity Photo 1.8,5 Designer 1.8.5 and Publisher 1.8.5 (mainly Photo), now ex-Adobe CC

CPU: AMD A6-3670. RAM: 16 GB DDR3 @ 666MHz, Graphics: 2047MB NVIDIA GeForce GT 630

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Thanks John,

This is a very interesting suggestion. It almost works. It gets rid, completely, of the common areas and that is great. However, it blends the areas that are different. Instead of a blend in the areas that are different, I want the pixels from the top layer only. This then represents the addition I had made in the collage.  Think of a big sheet of blue paper as my start. I photograph that and make it layer 1. Then I scatter some leaves on the blue paper, photograph it and make that layer 2. But I want to create (for future editing purposes) a layer that has only the leaves. (I could do it by selection but this can be tricky in my case.) Your suggestion obliterates the blue background and that it great. However, the bit left is a blend of the leaves and the blue that was behind the leaves.

However, it's a great idea and I will think some more along these lines.

Thank you.

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Dear John,

Thanks again. I did it, thanks to you.

Do what you said to get the difference. The common area is black (of course) so it's a trivial flood select then cut. This leaves the bit I want but with the wrong colors. Select that bit, set opacity to zero then merge it with the layer that had the correct colors. Then merge these layers. The selection stays through the merge and, since the selection came from that layer in the first place, it is exactly in the right position. This, of course, merges the colors but, since I set one to be totally transparent, the merged color is exactly what I want. Now I simply cut and paste into a new layer. While, in theory, I could have selected this in the first place, in the situations I have, it is very complex and would have taken forever. So this rouse is a way of selecting the difference between two layers (or many layers) when these differences are rather complax.

Couldn't have done it had you not set me off in the right direction.

Robin

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