New color conversion system

[Casper Boemann]

On Thursday 20 September 2007 10:19, Cyrille Berger wrote:
> Hello,
>
> While working on tone mapping for Krita, I was dramatically reminded of one
> of our short coming of our color conversion system. Most (not to say all)
> tone mapping algorithms work in XYZ float 32bit. But usually HDR pictures
> are in RGB. So the first step is to convert to XYZ, the problem is that
> currently, when a convertion involves a non LCMS colorspace, it fallback to
> converting to/from LAB integer 16bit. Meaning that for a HDR colorspace, we
> lose a lot of usefull information.
>
> I see three solutions:
>  * wait for lcms to support float colorspace (we might as well wait
> forever, from last news, it was a lot of work and Marti Maria don't seem to
> have much time currently)
>  * quick and dirty, do the fallback in LAB32Float
>  * leave to colorspace to define a list of convertion they can make, and
> have the possibility to link them. For instance, XYZf32 says he can convert
> to {XYZ16, RGB16f|32f} and RGB32f says he can convert to { RGB8 }
>
> So if we want XYZf32 to convert to RGB32f, the convertion will be handled
> by XYZf32 and it wouldn't lose the HDR information.
>
> This is a purely theorical case:
> But if we want to do XYZf32 to RGB8, the system will propose XYZf32 to
> RGB32f to RGB8 .
> The problem with that system is that if XYZ16f offers transformation to
> RGB8 (and it does as they are both lcms colorspace), then we have two
> options to convert XYZf32 to RGB8, either XYZf32 to RGB32f to RGB8 and
> XYZf32 to XYZ16 to RGB8. Ideally that would give the same results, but I am
> not so sure.
>
> This solution is more complicated, but it's also more or less how I
> understand lcms and other color management systems are working.
>
> So what do you think guys ?
How about switching pcs to XYZf32 rather than lab16. In the long run this will 
be more correct anyway.

I'm not sure we'll avoid multiple paths by this, but i think it solves our 
immediate problems for tonemapping
-- 
best regards / venlig hilsen
Casper Boemann