var colorspace = (function () {

var exports = {};

// Convert an sRGB value in [0, 255] to a linear intensity
// value in [0, 1].
//
// http://en.wikipedia.org/wiki/SRGB#The_reverse_transformation
exports.sRGB_to_linear = function (v) {
    v = v / 255.0;
    if (v <= 0.04045) {
        return v / 12.92;
    } else {
        return Math.pow((v + 0.055) / 1.055, 2.4);
    }
};

// Compute luminance (CIE Y stimulus) from linear intensity
// of sRGB / Rec. 709 primaries.
exports.rgb_luminance = function (channel) {
    return 0.2126*channel[0] + 0.7152*channel[1] + 0.0722*channel[2];
};

// Convert luminance (photometric, CIE Y)
// to lightness (perceptual, CIE L*)
//
// http://en.wikipedia.org/wiki/Lab_color_space#Forward_transformation
exports.luminance_to_lightness = function (luminance) {
    var v;
    if (luminance <= (216 / 24389)) {
        v = (841 / 108)*luminance + (4 / 29);
    } else {
        v = Math.pow(luminance, 1/3);
    }

    return 116*v - 16;
};

return exports;
}());