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.\" RCSid "$Id$" |
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.\" Print using the -ms macro package |
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.DA 11/13/2023 |
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.DA 12/09/2024 |
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.LP |
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.tl """Copyright \(co 2023 Regents, University of California |
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.tl """Copyright \(co 2024 Regents, University of California |
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.sp 2 |
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.TL |
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The |
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0 |
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3 red green blue |
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.DE |
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While alternate materials that are reflective will appear as normal, |
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indirect rays will use the mirror's reflectance rather than the |
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alternate type. |
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Transmitting materials are an exception, where both transmission and |
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reflection will use the alternate type for all rays not specifically |
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targeting virtual light sources. |
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Therefore, transmitting alternate types should only have pure specular |
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reflection if they reflect at all, to maintain a valid calculation. |
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.PP |
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The mirror material type reflects light sources only from the front side |
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of a surface, regardless of any alternate material. |
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If virtual source generation is desired on both sides, two coincident |
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surfaces with opposite normal orientations may be employed to achieve |
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this effect. |
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The reflectance and alternate material type may be |
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different for the overlapped surfaces, |
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and the two sides will behave accordingly. |
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.LP |
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.UL Prism1 |
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.PP |
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8 dred dgrn dblu sred sgrn sblu u-power v-power |
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.DE |
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.LP |
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.UL WGMDfunc |
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.PP |
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WGMDfunc is a more programmable version of trans2, |
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with separate modifier paths and variables to control each component. |
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(WGMD stands for Ward-Geisler-Moroder-Duer, which is the basis for |
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this empirical model, similar to the previous ones beside Ashik2.)\0 |
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The specification of this material is given below. |
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.DS |
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mod WGMDfunc id |
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13+ rs_mod rs rs_urough rs_vrough |
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ts_mod ts ts_urough ts_vrough |
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td_mod |
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ux uy uz funcfile transform |
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0 |
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9+ rfdif gfdif bfdif |
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rbdif gbdif bbdif |
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rtdif gtdif btdif |
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A10 .. |
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.DE |
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The sum of specular reflectance ( |
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.I rs |
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), specular transmittance ( |
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.I ts |
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), diffuse reflectance ( |
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.I "rfdif gfdif bfdif" |
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for front and |
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.I "rbdif gbdif bbdif" |
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for back) |
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and diffuse transmittance ( |
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.I "rtdif gtdif btdif" |
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) should be less than 1 for each |
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channel. |
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.PP |
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Unique to this material, separate modifier channels are |
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provided for each component. |
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The main modifier is used on the diffuse reflectance, both |
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front and back. |
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The |
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.I rs_mod |
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modifier is used for specular reflectance. |
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If "void" is given for |
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.I rs_mod, |
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then the specular reflection color will be white. |
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The special "inherit" keyword may also be given, in which case |
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specular reflectance will share the main modifier. |
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This behavior is replicated for the specular transmittance modifier |
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.I ts_mod, |
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which has its own independent roughness expressions. |
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Finally, the diffuse transmittance modifier is given as |
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.I td_mod, |
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which may also be "void" or "inherit". |
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Note that any spectra or color for specular components must be |
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carried by the named modifier(s). |
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.PP |
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The main advantage to this material over BRTDfunc and |
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other programmable types described below is that the specular sampling is |
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well-defined, so that all components are fully computed. |
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.LP |
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.UL Dielectric |
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.PP |
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A dielectric material is transparent, and it refracts light |
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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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The first two real arguments indicate the extrema of the |
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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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Subsequent real values correspond to multipliers at each wavelength. |
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The nmA wavelength may be greater or less than nmB, |
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but they may not be equal, and their ordering matches |
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the order 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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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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2+ sfunc 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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set in the evaluation context. |
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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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.LP |
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.UL Specdata |
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.PP |
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Specdata is like brightdata and colordata, but with more |
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than 3 specular samples. |
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.DS |
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mod specdata id |
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3+n+ |
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func datafile |
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funcfile x1 x2 .. xn transform |
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0 |
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m A1 A2 .. Am |
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.DE |
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The data file must have one more dimension than the coordinate |
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variable count, as this final dimension corresponds to the covered |
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spectrum. |
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The starting and ending wavelengths are specified in "datafile" |
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as well as the number of spectral samples. |
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The function "func" will be called with two parameters, the |
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interpolated spectral value for the current coordinate and the |
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associated wavelength. |
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If the spectrum is broken into 12 components, then 12 calls |
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will be made to "func" for the relevant ray evaluation. |
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.LP |
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.UL Specpict |
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.PP |
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Specpict is a special case of specdata, where the pattern is |
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a hyperspectral image stored in the common-exponent file format. |
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The dimensions of the image data are determined by the picture |
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just as with the colorpict primitive. |
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.DS |
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mod specpict id |
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5+ |
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func specfile |
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funcfile u v transform |
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0 |
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m A1 A2 .. Am |
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.DE |
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The function "func" is called with the interpolated pixel value |
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and the wavelength sample in nanometers, the same as specdata, |
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with as many calls made as there are components in "specfile". |
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.NH 3 |
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Mixtures |
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.PP |
