On 09/16/2011 02:20 AM, David Gowers (kampu) wrote:
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 <ofn...@laposte.net
<mailto:ofn...@laposte.net>> 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?
Well, I know that in "Normal" mode, I have in each RGB channel:
Composite=Over*alpha+Under(1-alpha)
(assuming "Under" is fully opaque), but in Subtract mode, I would have
several possibilities
Composite=Under(1-alpha)-Over*alpha
or
Composite=Under(1-alpha)+(1-Over)*alpha
or
Composite=Under(1-alpha)+(1-Over*alpha)
and $deity knows what else.
math.rb isn't taking the opacity in account (but is an interesting read...)
Thx.
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