Re: physical colors and Mathematica colors

*To*: mathgroup at smc.vnet.net*Subject*: [mg26405] Re: physical colors and Mathematica colors*From*: Lawrence Walker <lwalker701 at earthlink.net>*Date*: Wed, 20 Dec 2000 00:21:30 -0500 (EST)*Organization*: Morgan State University: COMSARE*References*: <91f7u4$55k@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi Mr. Nichols, I created a function. It still needs tweaking though. Below is an outline of how I created the SpectrumPlot function. Plot HUE from 0 to 1 using density plot Rescale HUE from 0 to about .9 so last color can be violet. Remap 0->.9 to 7500->3800 Angstroms. Create a function that will return a value for 'b' in Hue[h,s,b] that the edges of the sprectra will appear darken. Colors outside of the visible spectra should appear dark. Remap from the non-physical HUE[] generated colors to the corresponding colors that appear on the emission sprectra using the Interpolation function. This is very subjective. NonvisibilityValue[h_, rolloff_, lev_] := (* Return a value for 'b' in Hue[h, s, b] so that the edges of the sprectra will appear darken *) Module[{x0}, x0 = rolloff*Log[(1 - lev)/lev]; 1 - (1 + E^((h - x0)/rolloff))^(-1) - (1 + E^(-((-1 + h + x0)/rolloff)))^(-1)]; Plot[NonvisibilityValue[x, .05, .8], {x, 0, 1}, PlotRange -> {0, 1}]; dat = {{3800, 3800}, {4400, 4000}, {5300, 6000}, {5800, 6800}, {7500, 7500}}; (* A remapping from the nonphysical HUE[] generated colors to the corresponding colors that appear on the emission sprectra using the Interpolation function. This is very subjective. To generate a new 'dat' matrix first plot spectrum with the the entries in the left column the same as the right. *) ColorMap[x_] = Interpolation[dat, InterpolationOrder -> 1][x]; SpectrumPlot[sat_, bright_, lastColor_, rolloff_, lev_] := Module[{lam, h, x0}, DensityPlot[h = (7600 - ColorMap[lam])/3800; h, {lam, 3800, 7600}, {dum, 0, 1000}, Mesh -> False, Frame -> True, FrameTicks -> {Automatic, False}, PlotPoints -> {2000, 2}, AspectRatio -> Automatic, ColorFunction -> (Hue[# lastColor, sat, bright*NonvisibilityValue[#, rolloff, lev]] &)]]; SpectrumPlot[1, .9, .8, .05, .5]; Another trick might be to scan the actual picture to create a bitmap or gif file and then import the picture into Mathematica using the Import[] function. You should be able to splice the pixels into the corresponding physical colors and remap them directly to the Angstrom scale. I just might try this. Lawrence PNichols at cornell-iowa.edu wrote: > Dear Group, > > I am working on a package for which I need a function which takes a > wavelength of light (in nanometers, for example) and returns an RGBColor > specification. Has anyone made such a function for Mathematica? > > Of course, it is not essential that the result be RGBColor; any other > standard computer-graphics color model would do the job (HSB, HLS, CMY, > CMYK, etc.), because the conversions are standard. It's only the conversion > between one of these and physical wavelengths which I don't know. > > I understand that human color perception is a complicated matter, and so is > rendering of color on computer display devices. (The brightness dimension > is perhaps the most obvious ambiguity.) It's probably nonsense to ask for > a "perfect" correspondence between wavelength and RGB. But is there a > "standard" mapping? Or one that you think is "pretty good"? > > I shall be grateful for even the smallest suggestions. > > Preston Nichols > Visiting Assistant Professor of Mathematics > Cornell College > -- ------------------------------------------------------------ (\___/) The fear of the LORD is the beginning of (o\ /o) wisdom: a good understanding have all they /|:.V.:|\ that do his commandments: his praise \\:::::// endureth for ever. Psa 111:10 -----`"" ""`------------------------------------------------ Lawrence A. Walker Jr., M.Eng./Ph.D. Candidate Morgan State University Clarence M. Mitchell School of Engineering COMSARE (Center Of Microwave/Satellite And RF Engineering) Rm: 306-Schafer Phone: (443)885-1453 ------------------------------------------------------------