From English Wikipedia @ Freddythechick
local p = {}
local redvalue = 0
local greenvalue = 0
local bluevalue = 0
local function nm2RGB(wavelength, IFcorrect)
-- code based on an algorithm from Dan Bruton's Color Science Page: http://www.physics.sfasu.edu/astro/color/spectra.html
-- calculating RGB color components
if (wavelength >= 380) and (wavelength < 440) then
redvalue = (440 - wavelength) / 90
greenvalue = 0
bluevalue = 1
elseif (wavelength >= 440) and (wavelength < 490) then
redvalue = 0
greenvalue = (wavelength - 440) / 50
bluevalue = 1
elseif (wavelength >= 490) and (wavelength < 510) then
redvalue = 0
greenvalue = 1
bluevalue = (510 - wavelength) / 20
elseif (wavelength >= 510) and (wavelength < 580) then
redvalue = (wavelength - 510) / 70
greenvalue = 1
bluevalue = 0
elseif (wavelength >= 580) and (wavelength < 645) then
redvalue = 1
greenvalue = (645 - wavelength) / 65
bluevalue = 0
elseif (wavelength >= 645) and (wavelength <= 780) then
redvalue = 1
greenvalue = 0
bluevalue = 0
end
-- calculating intensity correction factor
if IFcorrect then
local intensityfactor = 0
if (wavelength >= 380) and (wavelength < 420) then
intensityfactor = 0.3 + 0.7*(wavelength - 350) / 70
elseif (wavelength >= 420) and (wavelength <= 700) then
intensityfactor = 1
elseif (wavelength > 700) and (wavelength <= 780) then
intensityfactor = 0.3 + 0.7*(780 - wavelength) / 80
end
redvalue = redvalue * intensityfactor
greenvalue = greenvalue * intensityfactor
bluevalue = bluevalue * intensityfactor
end
end
function p.emission(frame)
-- this function returns the string "#RRGGBB" with approximate RGB value for a wavelength passed as a first argument
local wavelength = tonumber(frame.args[1])
nm2RGB(wavelength, true)
local result='#' .. string.format("%.2X%.2X%.2X", 255*redvalue, 255*greenvalue, 255*bluevalue)
return result
end
local function absorption_to_visible(wavelength_abs)
-- code based on a color wheel drawn at: http://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/spectrpy/uv-vis/spectrum.htm
local wavelength_vis
local minVioletIndigo = 380 -- originally, it was 400
local maxVioletIndigo = 430
local widthVioletIndigo = maxVioletIndigo - minVioletIndigo
local minBlue = 430
local maxBlue = 490
local widthBlue = maxBlue - minBlue
local minGreen = 490
local maxGreen = 560
local widthGreen = maxGreen - minGreen
local minYellow = 560
local maxYellow = 580
local widthYellow = maxYellow - minYellow
local minOrange = 580
local maxOrange = 650 -- originally, it was 620
local widthOrange = maxOrange - minOrange
local minRed = 650 -- originally, it was 620
local maxRed = 780 -- originally, it was 800
local widthRed = maxRed - minRed
if (wavelength_abs>=minVioletIndigo) and (wavelength_abs<=maxVioletIndigo) then
wavelength_vis = (wavelength_abs - minVioletIndigo)*widthYellow/widthVioletIndigo + minYellow
elseif (wavelength_abs>minBlue) and (wavelength_abs<=maxBlue) then
wavelength_vis = (wavelength_abs - minBlue)*widthOrange/widthBlue + minOrange
elseif (wavelength_abs>minGreen) and (wavelength_abs<=maxGreen) then
wavelength_vis = (wavelength_abs - minGreen)*widthRed/widthGreen + minRed
elseif (wavelength_abs>minYellow) and (wavelength_abs<=maxYellow) then
wavelength_vis = (wavelength_abs - minYellow)*widthVioletIndigo/widthYellow + minVioletIndigo
elseif (wavelength_abs>minOrange) and (wavelength_abs<=maxOrange) then
wavelength_vis = (wavelength_abs - minOrange)*widthBlue/widthOrange + minBlue
elseif (wavelength_abs>minRed) and (wavelength_abs<=maxRed) then
wavelength_vis = (wavelength_abs - minRed)*widthGreen/(widthRed + 20) + minGreen
-- one of the "corrected" versions: wavelength_vis = (wavelength_abs - minRed - 30)*widthGreen/widthRed + minGreen
end
return wavelength_vis
end
local minAntiMagenta = 550
local maxAntiMagenta = 570
local function process_magenta(wavelength_abs)
local redvalue_RED
local bluevalue_RED
local greenvalue_RED
local redvalue_BLUE
local bluevalue_BLUE
local greenvalue_BLUE
local widthAntiMagenta = maxAntiMagenta - minAntiMagenta
local bias_BLUE = (wavelength_abs - minAntiMagenta)/widthAntiMagenta
local bias_RED = (maxAntiMagenta - wavelength_abs)/widthAntiMagenta
nm2RGB(700, false)
redvalue_RED = redvalue*bias_RED
bluevalue_RED = bluevalue*bias_RED
greenvalue_RED = greenvalue*bias_RED
nm2RGB(400, false)
redvalue_BLUE = redvalue*bias_BLUE
bluevalue_BLUE = bluevalue*bias_BLUE
greenvalue_BLUE = greenvalue*bias_BLUE
redvalue = 0.6+ 0.4*(redvalue_RED + redvalue_BLUE)
bluevalue = 0.7 + 0.3*(bluevalue_RED + bluevalue_BLUE)
greenvalue = greenvalue_RED + greenvalue_BLUE
end
function p.absorption(frame)
-- this function returns the string "#RRGGBB" with approximate RGB value for a complementary color (reflection) to a color, defined as a wavelength passed as a first argument
local wavelength = tonumber(frame.args[1])
-- adding magentas to smoothen red->blue transition. Trying 540..570 nm
if (wavelength>=minAntiMagenta) and (wavelength<=maxAntiMagenta) then
process_magenta(wavelength)
else nm2RGB(absorption_to_visible(wavelength), false)
end
local result='#' .. string.format("%.2X%.2X%.2X", 255*redvalue, 255*greenvalue, 255*bluevalue)
return result
end
return p
