Greg M. Johnson wrote:
> In Rune's file,  it looks like medium-bright areas
> get brighter, whereas, medium-dark areas get DARKER.

Yep, that's usually the point of contrast, isn't it? :)

Here's the logic behind the trick:

As we all know, if you use a transmit value between 0.0 and 1.0, then colors
seen through this pigment will get nearer to your specified rgb color.

If you use rgb 1.0 transmit 0.5 then all colors will get nearer to rgb 1.0.
If you use rgb 0.0 transmit 0.5 then all colors will get nearer to rgb 0.0.
If you use rgb 0.5 transmit 0.5 then all colors will get nearer to rgb 0.5.

The closer the transmit value is to 1.0, the less the colors seen through
the pigment will get near your specified rgb color. When transmit is 1.0,
then the colors seen through the pigment will not get near your specified
rgb color at all, but just stay the same.

Using a transmit value above 1.0 just extends the logic... The colors seen
through the pigment will *spread out* from your specified rgb color. And the
brighter the transmit value, the more the colors spread out.

If you use rgb 0.0 transmit 2.0 then all colors will spread out from rgb
0.0, that is, colors above 0.0 get brighter and colors below 0.0 get darker
(but you usually don't have negative colors in your scene).

If you use rgb 1.0 transmit 2.0 then all colors will spread out from rgb
1.0, that is, colors below 1.0 get darker and colors above 1.0 get brighter
(but they'll just appear to still be white).

If you use rgb 0.5 transmit 2.0 then all colors will spread out from rgb
0.5, that is, colors below 0.5 get darker and colors above 0.5 get brighter.
This is in effect a contrast filter that gives 2x contrast.

The trick works independently on red green and blue, so you can also get
special effects by using non-gray colors.

Rune
-- 
3D images and anims, include files, tutorials and more:
rune|vision:  http://runevision.com
POV-Ray Ring: http://webring.povray.co.uk

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