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Reference on Opacity variations in merging modes

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Reference on Opacity variations in merging modes Alchemie foto\\grafiche 24 Apr 16:35
  Reference on Opacity variations in merging modes David Gowers 24 Apr 17:13
Alchemie foto\\grafiche
2009-04-24 16:35:17 UTC (over 15 years ago)

Reference on Opacity variations in merging modes

I found the algorithms of many merging mode

BUT all the the formula there do not take opacity into account so as now the blending may be done only at 100% opacity (btw is for a "blending filter" , that allow to merge also in mode not available in Gimp obviously the result, the output is the visible from the the merging as new layer )

I'm sure somewhere in the Gimp code or documentation there is the answer: how ,mathematically variation of opacity are taken into account, but i am really lost in front of page of codes and doc

could someone ( help me, pointing to a specific page or speciphic doc

Also i need help to find found the algorithms and doc on modes as "erase" "color erase"" behind" (available for Edit/fade) and "grain extract" "grain merge" ?

Any help or pointer will be really appreciated

thank

David Gowers
2009-04-24 17:13:04 UTC (over 15 years ago)

Reference on Opacity variations in merging modes

On Sat, Apr 25, 2009 at 12:05 AM, Alchemie foto\grafiche wrote:

I found the algorithms of many merging mode

BUT all the the formula there do not take opacity into account so as now the blending may be done only at 100% opacity (btw is for a "blending filter" , that  allow to merge also in mode not available in Gimp  obviously the result, the output is the visible from the the merging as new layer )

I'm sure somewhere in the Gimp code or documentation there is the answer:  how ,mathematically variation of opacity are taken into account, but i am really lost in front of page of codes and doc

You should understand, that the new GEGL-based layer modes are subtly different from the legacy GIMP code in how they treat alpha. That said, app/gegl/gimpoperationpointlayermode.c contains all code dealing with layer compositing modes, and that is as simple as it gets.
Yes, I find it confusing too.