[Radiance-general] .pic precision

[Richard Murray]

I'm starting to use Radiance in research on visual perception of 3D 
shape.  The .pic file format assigns each colour channel one byte, plus 
a common exponent for all three, resulting in about 1% precision.  When 
testing peoples' ability to detect faint patterns, 1% isn't precise 
enough, e.g., humans can detect sine wave patterns at less than 1% 
contrast, but in the .pic format, a 1% amplitude sine wave would come 
out more like a square wave.

 From a quick look through rpmain.c and rpict.c, it looks like the the 
floating-point COLOR struct is used throughout the rendering 
calculations, and that the conversion to COLR is made at the very end, 
in fwritescan(), when writing the .pic file.  This suggests that I 
could just replace fwritescan() with a routine that writes the file at 
a higher precision.

My question is this:  are there other factors in the rendering 
calculations (rounding, etc.) that limit the precision to around 1% 
anyway?

Thanks,

Richard