ice-boy - Two things, in my mind. First is scarlock's point that the difference between Exponential and HSV Exponential is the color space they work in. For (RGB) Exponential, the transfer function I wrote down is applied to each of the R, G, and B axes separately, while for HSV Exponential, it is applied to the V axis only. The point of defining HSV coordinates in the first place is so that the perceptual qualities of Hue, Saturation and Value are decoupled from each other - changing one does not effect the other two. So, HSV Exponential compresses only the Value without changing the Hue or Saturation. For (RGB) Exponential, these perceptual qualities are cross-coupled; changing just R will change all three of HSV. Changing all three of RBG by the same factor will, I think, leave Hue the same, but mix Saturation and Value. Changing Value is equivalent to turning down the brightness of the lights and doing nothing else.

The second is that Tone Mapping is really quite different from Gamma Correction. The Gamma Correction transfer function is concentrated at the low end of the brightness scale; it works on the "toe" of the response curve. [For the ubertechies, the fact that the top value of the transfer function is pinned at 255 forces all the change with gamma to the low end of the transfer function.] If you look at the Tone Mapping transfer function, you'll see that is does practically nothing at the low end of the brightness scale but compresses the high end; it works on the "shoulder" of the response curve. As the Poser 8 documentation says, it is designed to simulate the saturation that happens in real film and avoid hard clipping of highlights in digital images.

My conclusion would be that Tone Mapping and Gamma Correction are very distinct things and you should not try to use one in place of the other. "Correct" usage uses both, and all the old GC discussion is still true.

Whichway