[Radiance-general] Re: where to get GretagMacbeth ColorCheck/ColorChecker

[Greg Ward]

> From: Randolph Fritz <randolph@panix.com>:
> Hey, Greg, have you considered adding ICC color profile support to some
> Radiance components, perhaps the PNG image conversion program?  That
> would allow Radiance users to make use of the tools that the various
> commerical graphic arts software people have developed; MacOS X and 
> some
> Windows users would--if their systems were properly set up--get the
> ability to print color predictably.  (Not sure if there's direct
> PostScript support for ICC color profiles.)
>
> Randolph

Color in rendering is an interesting problem.  The main source of color 
mismatches is going to be the relationship between the scene illuminant 
and the surface reflectances, which is of course ignored by ICC 
profiles.  The color space used by Radiance is close to the sRGB 
primaries, but not exactly those.  To convert to sRGB from a standard 
Radiance picture, use the following command:

	% ra_xyze -r -p .64 .33 .30 .15 .06 .313 .329 stand.pic | ra_tiff -g 
2.2 - srgb.tif

 From there, you should be able to print and get reliable color results 
on most systems, including Macs and PCs, since they assume sRGB given 
no other information.

However, the point I was trying to make was unless you have very 
carefully rendered your scene in order to arrive at the standard 
Radiance color space, these sorts of manipulations are futile.  To read 
in greater detail how to compute color correctly, including full 
spectral effects, see the recent paper I wrote with Elena 
Vileshin-Eydelberg:

	http://viz.cs.berkeley.edu/gwlarson/papers/egwr02/

This covers important issues such as white balance and optimal 
rendering color spaces.  Radiance can render in any RGB space you 
choose -- they are just three separate color channels as far as the ray 
tracer is concerned.

-Greg

P.S.  Have you ever taken a look at the ICC specification?  Eeeeeyuckkk!