[Bf-compositor] Question regarding changes to blending modes

[Kévin Dietrich]

Hi people, 

I'm currently writing a patch to rework the state of blending operations
inside of Blender. Right now the operations are defined in multiple
places around the code base so I thought it could be good to ease out
maintenance of that part of the code and to have them all defined in one
place. So far, so good. 

By running some speed-tests, out of curiosity, I noticed that (at least
in the compositor) the Hue, Saturation, Color and Value modes were the
slowest. And that is apparently due to multiple RGB <-> HSV conversions.
So I did some searches and found some interesting simple formulas which
do not rely on those conversions. 

Now, these modes are a little faster (~10-12%), but they do look a
little different than before, especially the Value blend mode(, and that
is a little strange). 

So the question is: would the users (especially module members) agree on
that change ? 

To have a look at the patch, or to test it, or just to see the
difference between the before and after for those above mentioned
operations, please head over to http://developer.blender.org/D539 . I
have uploaded there a few images demonstrating the changes. 

Sincerely, 

Kévin Dietrich. 
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