rgbhsl.lua

-- h, s, l, r, g, b, are all in range [0, 1]

local function hslToRgb(h, s, l)
    if s == 0 then return l, l, l end
    local function to(p, q, t)
        if t < 0 then t = t + 1 end
        if t > 1 then t = t - 1 end
        if t < .16667 then return p + (q - p) * 6 * t end
        if t < .5 then return q end
        if t < .66667 then return p + (q - p) * (.66667 - t) * 6 end
        return p
    end
    local q = l < .5 and l * (1 + s) or l + s - l * s
    local p = 2 * l - q
    return to(p, q, h + .33334), to(p, q, h), to(p, q, h - .33334)
end

local function rgbToHsl(r, g, b)
    local max, min = math.max(r, g, b), math.min(r, g, b)
    local b = max + min
    local h = b / 2
    if max == min then return 0, 0, h end
    local s, l = h, h
    local d = max - min
    s = l > .5 and d / (2 - b) or d / b
    if max == r then h = (g - b) / d + (g < b and 6 or 0)
    elseif max == g then h = (b - r) / d + 2
    elseif max == b then h = (r - g) / d + 4
    end
    return h * .16667, s, l
end