brettel_colorblind_simulation.js

// Code adapted from libDaltonLens https://daltonlens.org (public domain)

function linearRGB_from_sRGB(v)
{
    var fv = v / 255.0;
    if (fv < 0.04045) return fv / 12.92;
    return Math.pow((fv + 0.055) / 1.055, 2.4);
}

function sRGB_from_linearRGB(v)
{
    if (v <= 0.) return 0;
    if (v >= 1.) return 255;
    if (v < 0.0031308) return 0.5 + (v * 12.92 * 255);
    return 0 + 255 * (Math.pow(v, 1.0 / 2.4) * 1.055 - 0.055);
}

var brettelFunctions = {
    Normal: function (v) { return (v); },
    Protanopia: function (v) { return brettel(v, 'protan', 1.0); },
    Protanomaly: function (v) { return brettel(v, 'protan', 0.6); },
    Deuteranopia: function (v) { return brettel(v, 'deutan', 1.0); },
    Deuteranomaly: function (v) { return brettel(v, 'deutan', 0.6); },
    Tritanopia: function (v) { return brettel(v, 'tritan', 1.0); },
    Tritanomaly: function (v) { return brettel(v, 'tritan', 0.6); },
    Achromatopsia: function (v) { return monochrome_with_severity(v, 1.0); },
    Achromatomaly: function (v) { return monochrome_with_severity(v, 0.6); }
};

var sRGB_to_linearRGB_Lookup = Array(256);
(function () {
    var i;
    for (i = 0; i < 256; i++) {
        sRGB_to_linearRGB_Lookup[i] = linearRGB_from_sRGB(i);
    }

})();

brettel_params = {
    protan: {
        rgbCvdFromRgb_1: [
            0.14510, 1.20165, -0.34675,
            0.10447, 0.85316, 0.04237,
            0.00429, -0.00603, 1.00174
        ],
        rgbCvdFromRgb_2: [
            0.14115, 1.16782, -0.30897,
            0.10495, 0.85730, 0.03776,
            0.00431, -0.00586, 1.00155
        ],
        separationPlaneNormal: [ 0.00048, 0.00416, -0.00464 ]
    },

    deutan: {
        rgbCvdFromRgb_1: [
            0.36198, 0.86755, -0.22953,
            0.26099, 0.64512, 0.09389,
           -0.01975, 0.02686, 0.99289,
        ],
        rgbCvdFromRgb_2: [
            0.37009, 0.88540, -0.25549,
            0.25767, 0.63782, 0.10451,
           -0.01950, 0.02741, 0.99209,
        ],
        separationPlaneNormal: [ -0.00293, -0.00645, 0.00938 ]
    },

    tritan: {
        rgbCvdFromRgb_1: [
            1.01354, 0.14268, -0.15622,
           -0.01181, 0.87561, 0.13619,
            0.07707, 0.81208, 0.11085,
        ],
        rgbCvdFromRgb_2: [
            0.93337, 0.19999, -0.13336,
            0.05809, 0.82565, 0.11626,
            -0.37923, 1.13825, 0.24098,
        ],
        separationPlaneNormal: [ 0.03960, -0.02831, -0.01129 ]
    },
};

function brettel(srgb, t, severity) {
    // Go from sRGB to linearRGB
    var rgb = Array(3);
    rgb[0] = sRGB_to_linearRGB_Lookup[srgb[0]]
    rgb[1] = sRGB_to_linearRGB_Lookup[srgb[1]]
    rgb[2] = sRGB_to_linearRGB_Lookup[srgb[2]]
    
    var params = brettel_params[t];
    var separationPlaneNormal = params['separationPlaneNormal'];
    var rgbCvdFromRgb_1 = params['rgbCvdFromRgb_1'];
    var rgbCvdFromRgb_2 = params['rgbCvdFromRgb_2'];

    // Check on which plane we should project by comparing wih the separation plane normal.
    var dotWithSepPlane = rgb[0]*separationPlaneNormal[0] + rgb[1]*separationPlaneNormal[1] + rgb[2]*separationPlaneNormal[2];
    var rgbCvdFromRgb = (dotWithSepPlane >= 0 ? rgbCvdFromRgb_1 : rgbCvdFromRgb_2);

    // Transform to the full dichromat projection plane.
    var rgb_cvd = Array(3);
    rgb_cvd[0] = rgbCvdFromRgb[0]*rgb[0] + rgbCvdFromRgb[1]*rgb[1] + rgbCvdFromRgb[2]*rgb[2];
    rgb_cvd[1] = rgbCvdFromRgb[3]*rgb[0] + rgbCvdFromRgb[4]*rgb[1] + rgbCvdFromRgb[5]*rgb[2];
    rgb_cvd[2] = rgbCvdFromRgb[6]*rgb[0] + rgbCvdFromRgb[7]*rgb[1] + rgbCvdFromRgb[8]*rgb[2];

    // Apply the severity factor as a linear interpolation.
    // It's the same to do it in the RGB space or in the LMS
    // space since it's a linear transform.
    rgb_cvd[0] = rgb_cvd[0]*severity + rgb[0]*(1.0-severity);
    rgb_cvd[1] = rgb_cvd[1]*severity + rgb[1]*(1.0-severity);
    rgb_cvd[2] = rgb_cvd[2]*severity + rgb[2]*(1.0-severity);

    // Go back to sRGB
    return ([sRGB_from_linearRGB(rgb_cvd[0]),sRGB_from_linearRGB(rgb_cvd[1]),sRGB_from_linearRGB(rgb_cvd[2])]);
}

// Adjusted from the hcirn code
function monochrome_with_severity(srgb, severity) {
    var z = Math.round(srgb[0] * 0.299 + srgb[1] * 0.587 + srgb[2] * 0.114);
    var r = z*severity + (1.0-severity)*srgb[0];
    var g = z*severity + (1.0-severity)*srgb[1];
    var b = z*severity + (1.0-severity)*srgb[2];
    return ([r,g,b]);
}