Subject:
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Re: "Illusions"
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Newsgroups:
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lugnet.cad.ray
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Date:
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Tue, 2 Mar 2004 23:18:50 GMT
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Viewed:
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2033 times
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In lugnet.cad.ray, David Laswell wrote:
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In lugnet.cad.ray, Mike Thorn wrote:
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I was trying to make the flame pieces a little more transparent. I thought
there were a little too “strong.” It was just a little overbearing.
Unfortunately it didn’t quite work out - because raising the Transmit level
for some inexplicable reason turned the flame blue!
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Did you make it more transparent for the full spectrum, or just red and/or
green? If you didn’t increase the transparency for blue at the same time,
maybe it’s allowing orange light through while causing blue to reflect.
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The really strange thing, though, is that the shadows stayed orange and
the bowl reflects orange shapes.
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If my theory is correct, this is exactly what should happen.
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Well, it certainly sounds logical, but I thought that was what ‘filter’ did.
Well, let me have a look at the documentation.
...
Here we are:
The 4th component, called filter, specifies the amount of filtered transparency
of a substance. Some real-world examples of filtered transparency are stained
glass windows or tinted cellophane. The light passing through such objects is
tinted by the appropriate color as the material selectively absorbs some
frequencies of light while allowing others to pass through. The color of the
object is subtracted from the light passing through so this is called
subtractive transparency.
The 5th component, called transmit, specifies the amount of non-filtered light
that is transmitted through a surface. Some real-world examples of non-filtered
transparency are thin see-through cloth, fine mesh netting and dust on a
surface. In these examples, all frequencies of light are allowed to pass through
tiny holes in the surface. Although the amount of light passing through is
diminished, the color of the light passing through is unchanged.
The color of the object and the color transmitted through the object together
contribute 100% of the final color. So if transmit is set to 0.9, the
transmitted color contributes 90% and the color of the object contributes only
10%.
So it appears that we are experiencing a unique unknown phenomenon only
explainable through the explanation that the object in question was rendered by
a computer and therefore subject to incomprehensible quirks. ;)
But I’m still curious to know why it happened. I never touched the lights, so
they should still be fully white. There seems to be no logical reason why the
flames would appear blue.
-Mike
PS: Should anyone wish to build this thing, go for it:
http://www.brickshelf.com/gallery/Buachaille/Raytracing/brazier.ldr
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Message has 1 Reply:
 | | Re: "Illusions"
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| (...) I've never done CGI artwork before, so I couldn't say how this Filter function should work. I did, however, study theatrical lighting design in college, so I have some solid knowledge about how light works. For instance, if you place an object (...) (21 years ago, 3-Mar-04, to lugnet.cad.ray, FTX)
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Message is in Reply To:
| | Re: "Illusions"
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| (...) Did you make it more transparent for the full spectrum, or just red and/or green? If you didn't increase the transparency for blue at the same time, maybe it's allowing orange light through while causing blue to reflect. (...) If my theory is (...) (21 years ago, 2-Mar-04, to lugnet.cad.ray, FTX)
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