In article <39118632@news.povray.org> , "Rune" <run### [at] inamecom> 
wrote:

> I sometimes use transmitting surfaces for special effects.
> For example you can make a surface which inverts colors this way:

Well, it is more of a documentation problem:

"Each of the five components of a color are float values which are normally
in the range between 0.0 and 1.0. However any values, even negatives may be
used."

it should probably read:

"Each of the five components of a color are float values which are normally
in the range between 0.0 and 1.0. However any values, even negatives may be
used but proper operation can only be expected for values in the range
between 0.0 and 1.0. All other values do not model physical effects and
results may vary."

This is simply because what is a surface that inverts light? It does not
exist, there isn't a surface that increases the strength of light while it
is passing through it.
So there is no universal rule for such cases, and it really depends on the
implementation.  Most renderers will simply not allow you to specify such
values - POV-Ray does to give you greater artistic freedom.


     Thorsten

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