From lmarso@gmail.com Fri Jan  6 02:50:59 2006

Boudewijn and I discussed the potential utility of Krita to work on
curves for the channels of LAB colorspace, once the color
profile-aware color adjustment tool (temporarily out of CVS) is
restored to the build sources.

I have offered to write up what I know about the standard presentation
of LAB curves, e.g., in Photoshop, which is generally inverted from
lighter values on the lower left to darker values on the upper right,
and using color values from -128 to zero at midpoint to 128 (that's in
8 bit).

I presume the tool will initially work like the Cinepaint analogue,
doing a proper conversion in each direction, but without inverting the
curves or remapping the color values to the standard scale.

One thing I don't know is if you can resize the curves widget. 
Manipulations of curves in the A and B channels, in particular, often
require considerable precision in a small area around the center
point.  The ability to significantly enlarge the curves widget would
have great value.

I'll watch for the return of the color profile-aware color adjustment
tool code, and I'll try and help if anyone wants to move toward the
standard presentation of LAB from there.

Boudewijn and I also discussed the Photoshop "color picker" tool which
permits you to select a radius over which values are averaged.  In
addition, Photoshop lets you click on multiple points with values
you're focusing on for manipulation by curves.  You can click on and
save multiple averages, which appear one atop another.  Then, when you
manipulate the curves, a column appears alongside those saved
averages, and you can watch how your curve manipulations change the
average values.  It's sort of a "preview" of the effect of your curve
manipulations, expressed in color values averaged over a radius of
pixels.

For a full recitation of LAB colorspace manipulation and its power,
pick up Dan Margulis' "Photoshop LAB Color".
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