where to get GretagMacbeth ColorCheck/ColorChecker

From: Randolph Fritz <[email protected]>:
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!