Convert sRGB AdobeRGB

colorConvert.lua

-- Ported from the Python code of Mark Ransom
-- https://stackoverflow.com/a/40231268
-- For more on the magic numbers, see
-- http://brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html

ColorConvert = {}
ColorConvert.__index = ColorConvert

setmetatable(ColorConvert, {
    __call = function (cls, ...)
        return cls.new(...)
    end})

function ColorConvert.linear_sRGB(c)
    if c <= 0.04045 then
        return c / 12.92
    else
        return ((c + 0.055) / 1.055) ^ 2.4
    end
end

function ColorConvert.sRGB_to_XYZn(r, g, b)
    local Rlin = ColorConvert.linear_sRGB(r / 255.0)
    local Glin = ColorConvert.linear_sRGB(g / 255.0)
    local Blin = ColorConvert.linear_sRGB(b / 255.0)

    local Xn = Rlin * 0.4124 + Glin * 0.3576 + Blin * 0.1805
    local Yn = Rlin * 0.2126 + Glin * 0.7152 + Blin * 0.0722
    local Zn = Rlin * 0.0193 + Glin * 0.1192 + Blin * 0.9505

    return Xn, Yn, Zn
end

function ColorConvert.gamma_sRGB(c)
    if c <= 0.0031308 then
        return 12.92 * c
    else
        return 1.055 * (c ^ (1 / 2.4)) - 0.055
    end
end

function ColorConvert.XYZn_to_sRGB(Xn, Yn, Zn)
    local Rlin = Xn * 3.2406255 + Yn * -1.5372080 + Zn * -0.4986286
    local Glin = Xn * -0.9689307 + Yn * 1.8757561 + Zn * 0.0415175
    local Blin = Xn * 0.0557101 + Yn * -0.2040211 + Zn * 1.0569959

    local R = 255 * ColorConvert.gamma_sRGB(Rlin)
    local G = 255 * ColorConvert.gamma_sRGB(Glin)
    local B = 255 * ColorConvert.gamma_sRGB(Blin)

    if R < -0.0 then R = R - 0.5 elseif R > 0.0 then R = R + 0.5 end
    if G < -0.0 then G = G - 0.5 elseif G > 0.0 then G = G + 0.5 end
    if B < -0.0 then B = B - 0.5 elseif B > 0.0 then B = B + 0.5 end

    R = math.tointeger(R)
    G = math.tointeger(G)
    B = math.tointeger(B)

    return R, G, B
end

function ColorConvert.linear_AdobeRGB(c)
    if c <= 0.0 then
        return 0.0
    else
        return c ^ 2.19921875
    end
end

function ColorConvert.AdobeRGB_to_XYZn(R, G, B)
    local Rlin = ColorConvert.linear_AdobeRGB(R / 255.0)
    local Glin = ColorConvert.linear_AdobeRGB(G / 255.0)
    local Blin = ColorConvert.linear_AdobeRGB(B / 255.0)

    local Xn = Rlin * 0.57667 + Glin * 0.18556 + Blin * 0.18823
    local Yn = Rlin * 0.29734 + Glin * 0.62736 + Blin * 0.07529
    local Zn = Rlin * 0.02703 + Glin * 0.07069 + Blin * 0.99134
    
    return Xn, Yn, Zn
end

function ColorConvert.gamma_AdobeRGB(c)
    if c <= 0.0 then
        return 0.0
    else
        return c ^ (1 / 2.19921875)
    end
end

function ColorConvert.XYZn_to_AdobeRGB(Xn, Yn, Zn)
    local Rlin = Xn * 2.04159 + Yn * -0.56501 + Zn * -0.34473
    local Glin = Xn * -0.96924 + Yn * 1.87597 + Zn * 0.04156
    local Blin = Xn * 0.01344 + Yn * -0.11836 + Zn * 1.01517

    local R = 255 * ColorConvert.gamma_AdobeRGB(Rlin)
    local G = 255 * ColorConvert.gamma_AdobeRGB(Glin)
    local B = 255 * ColorConvert.gamma_AdobeRGB(Blin)

    if R < -0.0 then R = R - 0.5 elseif R > 0.0 then R = R + 0.5 end
    if G < -0.0 then G = G - 0.5 elseif G > 0.0 then G = G + 0.5 end
    if B < -0.0 then B = B - 0.5 elseif B > 0.0 then B = B + 0.5 end

    R = math.tointeger(R)
    G = math.tointeger(G)
    B = math.tointeger(B)

    return R, G, B
end

function ColorConvert.sRGB_to_AdobeRGB(r, g, b)
    Xn, Yn, Zn = ColorConvert.sRGB_to_XYZn(r, g, b)
    return ColorConvert.XYZn_to_AdobeRGB(Xn, Yn, Zn)
end

function ColorConvert.AdobeRGB_to_sRGB(r, g, b)
    Xn, Yn, Zn = ColorConvert.AdobeRGB_to_XYZn(r, g, b)
    return ColorConvert.XYZn_to_sRGB(Xn, Yn, Zn)
end

return ColorConvert