>    I suppose the fundamental question would then be: "If I say to povray
> to produce a linear gradient, should it produce a gradient which is
> linear according to light intensity, or according to the perceived
> linearity as seen by people?"

Agreed, as I wrote already it might be a good idea for an additional 
keyword (to be used in colour maps) that specifies whether you want 
physical linear interpolation (which will "look" non-linear) or some 
other interpolation type suited to the human visual system.  This would 
be totally separate to any gamma settings, as it has nothing to do with 
gamma.

For grey-scales you can already simply use something like "poly_wave 3" 
to get a more natural gradient, but once colours are involved it's going 
to look wrong without some more sophisticated interpolation algorithm.

>    As for whether eg. surface shading looks more realistic with the new
> gamma handling or the old one, it would be interesting to see some
> actual comparisons with photographs.

The problem with that kind of test is that you are also testing the 
surface lighting equations used in POV (which are a simplification of 
real surfaces).  I wasn't aware there was any doubt as to whether the 
new gamma was more accurate (you can simply test it with a black/white 
checkerboard next to 50% grey).

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