Re: [Gimp-developer] Some blend modes break in unbounded mode sRGB

[Elle Stone <ellestone ninedegreesbelow com>]

On 04/12/2014 06:45 PM, Øyvind Kolås wrote:
> On Fri, Apr 11, 2014 at 11:54 PM, Elle Stone
> <ellestone ninedegreesbelow com> wrote:
> > On 04/09/2014 06:36 PM, Elle Stone wrote:
> > > For Lighten only, Darken only, Multiply, Divide, and some of the other
> > > blend modes, results are *highly dependent* on the color space in which
> > > the blending is done. Removing clipping code doesn't fix the problem.
>
> You seem to be under the impression that all processing whatever the
> operation is done going to happen in one color space/pixel format a
> "working space". In a GEGL processing world; it is the individual
> operations that have working spaces; there is no global working space
> that things happen in. (NB: having gamma toggles in blending modes of
> GIMP is according to this model making things confusing, compositing
> in different color spaces should be _different_operations_).

I think you might be using the phrases "color space" and "working space" 
in a way that, although technically correct, perhaps might be confusing 
to a lot of people.

My understanding of what you mean by "color space/working space" is as 
follows:

In the strongly color-managed world of BABL and GEGL, the only *RGB* 
color space/working is *s*RGB, either the linear gamma/light sRGB or the 
more perceptually uniform regular sRGB with its not quite gamma=2.2 TRC.

And then there is:

sRGB converted to CIELAB.
sRGB converted to HSL.
sRGB converted to HSV.
sRGB converted to CMY(K).
sRGB converted to Gray.
sRGB converted to YCbCr.
sRGB converted to some other model of color space, such as XYZ or 
CIELUV, for which code might be written at some point in the future.

The key point is that the chromaticities of the *RGB* color space, that 
might be converted to some other *model* of color space, are *always* 
the *s*RGB chromaticities.

Is what I just wrote accurate? if yes, please confirm, If not, please 
explain where my understanding has gone awry.

I've asked this question of what is actually meant by "color 
space/working space" in the world of BABL and GEGL twice before now, and 
no one has answered. But it's a pretty important point, so I'm asking again.

Thanking you in advance for confirmation/clarification of what "color 
space/working space" means when discussing *BABL/GEGL* color 
spaces/working space,

Elle