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- Newsgroups: comp.graphics
- Path: sparky!uunet!ukma!darwin.sura.net!zaphod.mps.ohio-state.edu!uunet.ca!cognos!faraghec
- From: faraghec@cognos.com (Chad Faragher)
- Subject: Re: Is POV optically accurate ?
- Message-ID: <1992Nov13.152734.6675@cognos.com>
- Organization: Cognos Incorporated, Ottawa CANADA
- References: <1992Nov12.133317.5833@genes.icgeb.trieste.it> <1992Nov12.181351.23378@nas.nasa.gov>
- Date: Fri, 13 Nov 1992 15:27:34 GMT
- Lines: 39
-
- In article <1992Nov12.133317.5833@genes.icgeb.trieste.it> oberto@genes.icgeb.trieste.it (Jacques Oberto) writes:
- >I am trying to reproduce one of Newton's experiments with POV.
- >Would a simulated white light beam hitting a glass prism with the
- >right angle be scattered into a rainbow spectrum ?
- >Are POV and other ray-tracers optically accurate in that respect ?
- >Has anybody tested the properties of 'raytraced' light other than
- >reflection and refraction ?
-
- NO, POV is not accurate. (I can't speak for other ray tracers)
-
- In POV, white light is composed of a RED source a GREEN source and a BLUE
- source, as opposed to true "White" light which is composed of light of all
- visible frequencies.
-
- Also, POV's refraction does not depend on the frequency of the light. In
- fact at no point in the program does POV convert RGB to frequency. The
- Red, Green, and Blue light intensities are bundled up into an abstraction
- called "colour". All three beams of move together not as a wave of light,
- but throught a single mathematical abstraction called a "Ray". The ray
- is geometrically projected as a single entity, then a "colour" is assigned
- to it when it hits something.
-
- Also don't try anything with interference patterns, that's not implemented
- either. Forget about Newton's Rings, and don't look for colour fringing
- on a fish in a fishbowl.
-
- If you want to do Newtonian Optics with a ray tracer, the "colour" abstraction
- must be more true to life. Keep in mind that the RGB representation of colour
- was chosen because the eye perceives all colours as combinations of these.
- It can let you see any colour, but it does not represent the colour properties
- of light (frequency properties). A more suitable representation would
- require colour to be a spectrogram, clearly indicating which frequencies of
- light are present. Perhaps a list of hi,lo ranges would be a good data
- structure for this becuase one ray would have to be traced for each frequency.
-
- If someone writes a raytracer to do this, lemme know. Some algorithms to
- convert between Frequency and RGB may be of interest here too.
-
- Chad Faragher -- faraghec@cognos.com
-