On 2009-10-03, yahvuu <yah...@gmail.com> wrote:
> Using an analogy, the current situation for blending is like not
> having the curves tool, but only preset curves to choose from. And
> indeed there's a relation between curves and blending, for each RGB
> blend mode can be described as a set of 256 curves, at least within
> 8bit-accuracy.

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"A curve" is a function of one variable. "A layer mode" is a function
of two variables ("value" of a current level, and "value" of the
composite of levels below it; here "value" is, typically, the level of
R/G/B considered separately).
[Here I assume Porter-Duff semantic of layer modes, so transparency
is handled "automatically" when a function of 2 variables is
given. Otherwise (as with Dissolve) it is two functions of 4
variables: given levels and transparency of this level, and those
of the composite below, one gets new level and new transparency.]
The problem with your proposal is 2-fold:
1) "Invert" is just a particular case of an "apply-curve"; let's
remove this redundant misfeature;
1') Likewise for "levels".
2) More seriously: a graph is a convenient down-to-earth
representation of a function of one variable. It allows a simple
intuitive concept of direct manipulation.
I never saw a similar in convenience UI to directly manipulate a
function of two variables.
Hope this helps,
Ilya
P.S. When GIMP has a JIT compiler present, there would be no
significant problem in representing "a layer mode" as "a
programming language CODE" implementing a function of two
variables. [Note similarity with how shaders in OpenGL work...]
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