[Radiance-general] Re: Color appearance and color temperature

Thu, 14 Feb 2002 16:51:07 +0200

Thank you, this was very useful.

May I ask some related questions (sorry, they may be trivial but I did not 
find answers from the documentation):

Since Radiance has its own RGB definition, I tried to find out what is the 
RGB gamut produced by ra_tiff. Is it sRGB of something else? (pcond seems 
to produce sRGB as a default - am I right?). I am using the DOS/Windows 
executables. Is the resulting RGB gamut same for all systems?

Regards, Markku

At 22:46 2002-02-09 -0800, you wrote:
>The pcomb program provides for arbitrary color transforms, among other 
>things.  It's not the most efficient way to apply a 3x3 color matrix to an 
>image, but it works.  You just have to write out the equations for it, for 
>example:
>
>pcomb -f myclrmat.cal -e 'ro=Mrr*ri(1)+Mrg*gi(1)+Mrb*bi(1)' \
>                 -e 'go=Mgr*ri(1)+Mgg*gi(1)+Mgb*bi(1)' \
>                 -e 'bo=Mbr*ri(1)+Mbg*gi(1)+Mbb*bi(1)' inp.pic > out.pic
>
>The file myclrmat.cal contains the above coefficients, something like:
>
>{ Color transformation coefficients }
>Mrr : 1.25; Mrg : .21; Mrb : -.07;
>Mgr: .10; Mgg : 1.13; Mgb : .10;
>Mbr: -.11; Mbg : .03; Mbb : .97;
>
>These values are totally made up -- use whatever you like.  The ':' makes 
>the calculation slightly more efficient since it declares the values are 
>constant, and is preferred unless you want the coefficients to vary 
>somehow over the image.  It's probably better to put the formulas I have 
>on the pcomb command line directly into the myclrmat.cal file.  I just 
>wrote it this way for illustration purposes.
>
>There are of course a million things you can do with pcomb, at least.
>Color transforms are among the more mundane applications of a programmable 
>image filter, but the are useful.  If you have many such transforms to do, 
>you might want to write a special-purpose program that would be faster at it.
>
>-Greg
>
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Markku_Norvasuo
Technical_Research_Centre_of_Finland