Cousin Ricky <ric### [at] yahoocom> wrote:
>
> So I wrote a scene to render some of the grays with different gamma
> configurations under different POV-Ray versions, then sampled the output
> images and created montages with the sampled values...

Getting back to your original post here, about the slight discrepancies in color
values among the various versions of POV-ray:

I did some *basic* tests, solely in v3.8, using a simple pigment plus the
eval_pigment{...) macro, and I still get slight discrepancies in compared color
values. It somehow comes from the use of  srgb  vs.  rgb  in a color, AND on the
assumed_gamma of the scene.

#declare PIG_C = pigment{rgb <.75,.75,.75>} // CHANGE this from srgb to rgb

#debug concat("\n","PIGMENT_C evaluation = <",vstr(3,eval_pigment(PIG_C,
<.2,.2,.2>),", ",0,6),">","\n\n")

The various results using different assumed_gamma values:
--- With assumed_gamma 1.0:
1) using srgb: eval_pigment = <0.522522,0.522522,0.522522> // correct
2) using rgb:  eval_pigment = <0.750000,0.750000,0.750000> // correct
--- With assumed_gamma 2.2:
// 1) using srgb: eval_pigment = <0.744501,0.744501,0.744501> // ??
// 2) using rgb:  eval_pigment = <0.750000,0.750000,0.750000>
--- with assumed_gamma srgb:
// 1) using srgb: eval_pigment = <0.750000,0.750000,0.750000>
// 2) using rgb:  eval_pigment = <0.750000,0.750000,0.750000>

Under assumed_gamma 1.0, the evaluated values are correct. But under
assumed_gamma 2.2, the result with srgb is *slightly* off from the original
value. I have no idea why. (I would have thought that those two values would be
MUCH different, like under assumed_gamma 1.0).

Post a reply to this message