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.\" RCSid "$Id$" |
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.\" Print using the -ms macro package |
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< |
.DA 5/11/2023 |
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> |
.DA 11/13/2023 |
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.LP |
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.tl """Copyright \(co 2023 Regents, University of California |
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.sp 2 |
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font such as hexbit4x1.fnt, calls for uniform spacing. |
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Reasonable magnitudes for proportional spacing are |
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between 0.1 (for tightly spaced characters) and 0.3 (for wide spacing). |
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.LP |
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.UL Spectrum |
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.PP |
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The spectrum primitive is the most basic type for introducing spectral |
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color to a material. |
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Since materials only provide RGB parameters, spectral patterns |
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are the only way to superimpose wavelength-dependent behavior. |
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.DS |
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mod spectrum id |
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0 |
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0 |
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5+ nmA nmB s1 s2 .. sN |
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.DE |
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The first two real arguments indicate the limits of the covered |
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spectral range in nanometers. |
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Subsequent real values correspond to multipliers in each wavelength band, |
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where the first band goes from nmA to nmA+(nmB-nmA)/N, and N is the |
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number of bands (i.e., the number of real arguments minus 2). |
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The nmA wavelength may be greater or less than the nmB wavelength, |
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but they may not be equal, and their ordering must correspond to |
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the ordering of the spectral values. |
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A minimum of 3 values must be given, which would act |
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more or less the same as a constant RGB multiplier. |
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As with RGB values, spectral quantities normally range between 0 |
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and 1 at each wavelength, or average to 1.0 against a standard |
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sensitivity functions such as V(lambda). |
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The best results obtain when the spectral range and number |
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of samples match rendering options, though resampling will handle |
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any differences, zero-filling wavelenths outside the nmA to nmB |
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range. |
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A warning will be issued if the given wavelength range does not |
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adequately cover the visible spectrum. |
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.LP |
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.UL Specfile |
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.PP |
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The specfile primitive is equivalent to the spectrum type, but |
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the wavelength range and values are contained in a 1-dimensional |
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data file. |
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This may be a more convenient way to specify a spectral color, |
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especially one corresponding to a standard illuminant such as D65 |
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or a library of measured spectra. |
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.DS |
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mod specfile id |
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1 datafile |
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0 |
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0 |
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.DE |
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As with the spectrum type, rendering wavelengths outside the defined |
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range will be zero-filled. |
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Unlike the spectrum type, the file may contain non-uniform samples. |
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.LP |
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.UL Specfunc |
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.PP |
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The specfunc primitive offers dynamic control over a spectral |
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pattern, similar to the colorfunc type. |
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.DS |
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mod specfunc id |
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2+ sval funcfile transform |
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0 |
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2+ nmA nmB A3 .. |
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.DE |
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Like the spectrum primitive, the wavelength range is specified |
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in the first two real arguments, and additional real values are |
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accessible to the sval function. |
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This function is fed a wavelenth sample |
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between nmA and nmB as its only argument, |
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and it returns the corresponding spectral intensity. |
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.NH 3 |
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Mixtures |
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.PP |
