I remember there was some stuff on the old vfxpedia wishlist about merge modes... I'll just copy&paste from
here, maybe it adds to the discussion :
- Add more modes to Merge, at least a superset of the Bol tool. The Bol doesn't respect transformation or image scale, but sometimes I need to use those modes between images that are not perfect per-pixel matches. While Lighten is a substitute for Maximum, there's nothing suitable to replace Or, XOr, Divide, etc. --Chad 10:25, 12 October 2009 (EDT)
- Nuke has two merge modes that I found to be quite useful for combining flames or fog in linear colorspace: "hypot", which is the pythagorean theorem's sqrt(A*A + B*B) and "geometric" which uses 2*A*B/(A+B) to merge the images. Would be nice to have them without resorting to a custom tool. --Tilt 08:46, 9 June 2010 (EDT)
- Merge "Under" (over with Bg and Fg swapped) would be nice, in case you can't swap the inputs of the merge node (you might want to control which branch gets shown when Blend == 0 or which metadata gets passed to the output) --Tilt 14:20, 7 April 2013 (EDT)
About incorporating modes from ChBol into Merge: There's also this bit about the different naming of modes in merge, matte control and masks:
Right now, mask tools, the matte control tool and the merge node are allowing different operations or are using different names for the same thing:
- Code: Select all
Masks: Matte Control: Merge:
Merge Or Merge Over
Multiply And Merge In
Invert N/A Merge Xor
Add Add Merge with alpha gain == 0
N/A Inverse Subtract N/A
Merge with N/A Merge Held Out
Invert, then
inverting
the result
Multiply + N/A Merge Held Out with
Invert inputs swapped (stencil in Nuke)
Add and subtract create harsher results when used to combine to soft edges and these modes will result in values < 0 or > 1 when used in float mode. Multiplying and merging are the better solutions but are not available in every tool that would benefit from them. In this context, Nuke's inverse modes which swap FG and BG (like stencil vs. held out, mask vs. in) prove useful, and maybe Fusion could implement them too. The reason: it's not always possible to swap the inputs (masks can't swap inputs, but also merges when the BG's metadata is needed downstream or you want control over what gets passed through when the node is disabled). --Tilt 13:28, 2 June 2011 (EDT)