Hello all,
I've joined up with this list to make an important suggestion for improvement.
In short, the Color and Value blending, transfer modes in GIMP do not work as
they should. The problem is compounded by the fact that there seems to be no
application on Linux where these transfer modes work correctly. In fact, it
seems all the major applications use the same or very similar algorithms. So
the problem is the same in Krita (which uses GEGL as far as I know) and in
ImageMagick.
To confirm the problem, try this:
* Open an image in GIMP, preferrably one that has noticeable noise, and the
noise should be coloured, not merely monochromatic.
* Duplicate the image into a new layer and blur it, say by 5 points.
* Set the transfer mode of the blurred layer to Color.
What should happen is that the colour component of the noise should be
eliminated, but the luminance/value should remain the same. This is not the
case, the result worsens the luminance noise! If you have trouble seeing this,
zoom into the image up to 400% or try an image with more obvious noise. Also,
try increasing the blur factor.
Now by comparison, repeat the experiment in Photoshop. You won't fail to notice
that in Photoshop this works correctly. The colours are more muted, perhaps
'leaking' over colour boudaries, but the luma noise is not made worse.
The same effect is at play the other way round, if Value is used instead of
Color (and it's the bottom layer that is blurred). And the same effect is also
at play if instead of layer blending, the blending is done in the Fade command
dialog.
In short, there is no correct way yet of using these transfer modes on Linux and
a proper solution is desperately needed.
By the way, I'm using GIMP 2.6.8. I appreciate that 2.7.1 is using GEGL as will
2.8, but I doubt that will in itself offer the solution, because Krita is using
GEGL and the problem there is the same.
Thank you for listening and good luck with the coding.
Charlie
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