On Sat, Sep 17, 2011 at 8:36 AM, Ofnuts <ofnuts@xxxxxxxxxxx> wrote:
On 09/16/2011 02:20 AM, David Gowers (kampu) wrote:Well, I know that in "Normal" mode, I have in each RGB channel:In GEGL, the layer mode code is autogenerated from formula strings -- see operations/generated/math.rb
The opacity behaviour is not documented there, but my understanding is that the alpha of the underlying composite is preserved, and opacity only effects how much of the layer's COLOR channels are applied (per the standard blending formula).
On Fri, Sep 16, 2011 at 7:09 AM, Ofnuts <ofnuts@xxxxxxxxxxx> wrote:
I'll trying to find out what happens when a layer is in subtract mode
with a global opacity not one or zero (i.e. what computations are done
with the pixels values of the composite image of the layers below, the
pixel values of the layer, and the general opacity). I have a git
extract of the Gimp source code (and of gegl & babl) but got lost... Can
someone help?
Composite=Over*alpha+Under(1-alpha)
(assuming "Under" is fully opaque), but in Subtract mode, I would have several possibilities
No, you just subtract Over from Under with no multiplication, then you perform a RGB (not RGBA) Composite of the result and Under, to produce the final composite.
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