[Bf-committers] Color to greyscale conversion - confusion

Dahlia Trimble dahliatrimble at gmail.com
Tue Jun 26 22:22:03 CEST 2012

Color perception is unfortunately not simple. The spectral distribution of
the light illuminating a scene is highly variable in nature and is a strong
contributor to what colors we see and how bright different wavelengths
appear. There are also variations in the distribution of the cones in our
eyes that see different portions of the visible spectrum. Color spaces used
in computer graphics are often nonlinear. Any color manipulation in
computer graphics is only a approximation, and these approximations can be
improved with more sophisticated color management schemes which often use
large 3-dimensional lookup tables and interpolation techniques.
Unfortunately a simple 3 term linear conversion such as the existing
functions in blender are wrong, and changing a few values here and there
will not make them any more correct, because as soon as the illumination or
the surrounding scenery changes, perception changes. A 3-slider interface
that allows user tweaking of these values may be seen as an improvement but
is unfortunately dependent on the perception of the user who is
manipulating them. This allows more flexibility but is not correct as there
are still non-linearities in color spaces.

A more "correct" wan may be to have a user manipulated 3-term spine graph,
similar to the Image->Adjustments->Curves... dialog in Photoshop, with
appropriate defaults this may at least allow for correction of gross errors
or non-linearities. Then again, probably few of us would notice the subtle
improvements such flexibility would allow, and if one really wanted a high
quality conversion it could be done in an application specifically designed
for such a task prior to adding it to a Blender scene.

I would tend to agree with Campbell about not changing any conversions
which may drive effects such as displacement maps. Perhaps the functions in
question could be renamed to better describe how they are used in other
parts of blender, and documented as Campbell suggested. I don't think
there's goring to be a "correct" solution that uses 3 linear terms and a
"proper" solution will likely require significant of expertise and effort.

On Mon, Jun 25, 2012 at 2:50 PM, Knapp <magick.crow at gmail.com> wrote:

> I really like the idea of having a node that lets you adjust the rgb
> scalars. Perhaps it would have presets for newbies based on the
> standards.
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