This is more complicated than you think.
Do you really need to convert to HSL, manipulate, then convert back to RGB? Or
is enough to just be able to compute the luminance for each pixel and then do
scaling based on that? (Am I wrong to think that once you know the scaling
factor, you can apply that to each of the original channels independently?)
The formula for luminance depends on what color space you think the RGB
represents. If you think you have linear RGB in Rec709 space (not a bad
default assumption), then I believe the formula is that
L = 0.212507 * R + 0.71535 * G + 0.0721427 * B
But if you really wanted to be pedantic about it, you'd want this adjusted for
other color systems.
(Jeremy, if OCIO doesn't provide basic color utilities, such as conversion
between RGB and other handy non-spectral color spaces, or calculating luminance
in a color-aware way, perhaps it should? Or is that intentionally beyond the
scope of OCIO's design?)
On Jun 27, 2012, at 3:40 AM, Stefan Stavrev wrote:
> I need to go RGB <-> HSI, internally only for the algorithms.
>
> I also found this in the "enhancment" list for OIIO:
>
> https://github.com/OpenImageIO/oiio/issues/193
>
> Jeremy, maybe if you have such optimized conversion functions already,
> I could use them?
>
> Thanks
>
--
Larry Gritz
l...@larrygritz.com
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