Re: reversable, but not 1D color transforms in config.ocio


Andrew Wood <andre...@...>
 

You all are my heros.  I had gotten so caught up in the XYZ to LAB calculation that I didn't notice it could be reduced to a 1d LUT and simple matrix.

Troy, I was looking through your (amazing) example, and the only part that I didn't recognize was the matrix you used to go from RGB to XYZ based on srgb d65 primaries.  I usually steal my matrices from Bruce Almighty:

http://www.brucelindbloom.com/Eqn_RGB_XYZ_Matrix.html

but yours looks a little different from this one.  What is it based on?



On Saturday, February 4, 2017 at 10:13:36 PM UTC-8, Troy James Sobotka wrote:
Whilst stranded in an airport...


No assurances expressed or implied. Seems the values are darn close to Lindbloom's, which may account for a different value for Illuminant C adaptation via Bradford.

With respect,
TJS

On Sat, Feb 4, 2017 at 11:58 AM doug <col...@...> wrote:
The conversion from XYZ to CIELab can be done with matrices and 1d-LUTs, so you should be able to do the forward and reverse quite exactly with the existing machinery and without resorting to 3d-LUTs.

(Of course CIELab is only appropriate for display-referred colors, but that is a separate issue.)

Doug Walker

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