chroma-js/src/converter/in/hsi2rgb.coffee

JavaScript library for color conversions

# @requires utils

hsi2rgb = (h,s,i) ->
    ###
    borrowed from here:
    http://hummer.stanford.edu/museinfo/doc/examples/humdrum/keyscape2/hsi2rgb.cpp
    ###
    args = unpack arguments
    [h,s,i] = args

    # normalize hue
    #h += 360 if h < 0
    #h -= 360 if h > 360
    h /= 360
    if h < 1/3
        b = (1-s)/3
        r = (1+s*cos(TWOPI*h)/cos(PITHIRD-TWOPI*h))/3
        g = 1 - (b+r)
    else if h < 2/3
        h -= 1/3
        r = (1-s)/3
        g = (1+s*cos(TWOPI*h)/cos(PITHIRD-TWOPI*h))/3
        b = 1 - (r+g)
    else
        h -= 2/3
        g = (1-s)/3
        b = (1+s*cos(TWOPI*h)/cos(PITHIRD-TWOPI*h))/3
        r = 1 - (g+b)
    r = limit i*r*3
    g = limit i*g*3
    b = limit i*b*3
    [r*255, g*255, b*255, if args.length > 3 then args[3] else 1]