Am I in the right forum, or should this query be posted elsewhere?

What happens when you merge layers [image, not fill or adjustment] in Photoshop? The qualitative answer seems to be: WYSIWYG. But I am looking for a quantitative answer. I am looking for a precise - mathematical, if you will - description of the effect of the Photoshop Merge command.

Suppose I have two layers, 1 on top and 2 below it, and consider a position [pixel] P where the RGB intensities [on the usual 0-255 scale] are (r1, g1, b1) in layer 1 and (r2, g2, b2) in layer 2. Opacities are t1 and t2 [on the usual 0-100% scale].

Both layers are visible. Layer 1 is active. When I merge the two layers, the RGB intensities at the position P will be

(r,g,b).

My question: how is r related to r1,t1,r2,t2 ? And likewise for b and g.

What happens if I merge three layers?

Thanks in advance for all the erudite responses that will doubtless be forthcoming.

Ben Winter

What happens when you merge layers [image, not fill or adjustment] in Photoshop? The qualitative answer seems to be: WYSIWYG. But I am looking for a quantitative answer. I am looking for a precise - mathematical, if you will - description of the effect of the Photoshop Merge command.

Suppose I have two layers, 1 on top and 2 below it, and consider a position [pixel] P where the RGB intensities [on the usual 0-255 scale] are (r1, g1, b1) in layer 1 and (r2, g2, b2) in layer 2. Opacities are t1 and t2 [on the usual 0-100% scale].

Both layers are visible. Layer 1 is active. When I merge the two layers, the RGB intensities at the position P will be

(r,g,b).

My question: how is r related to r1,t1,r2,t2 ? And likewise for b and g.

What happens if I merge three layers?

Thanks in advance for all the erudite responses that will doubtless be forthcoming.

Ben Winter

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