Perceptual Transforms, Cont.

perceptualTransform2.cs

static Vector4 LinearToXyz (in Color c)
{
    // This could also be written as matrix-vector multiplication.
    // Perceptual luminance is the y component.
    return new Vector4 (
        0.41241086f * c.r + 0.35758457f * c.g + 0.1804538f * c.b,
        0.21264935f * c.r + 0.71516913f * c.g + 0.07218152f * c.b,
        0.019331759f * c.r + 0.11919486f * c.g + 0.95039004f * c.b,
        c.a);
}

static Vector4 XyzToCieLab (in Vector4 xyz)
{
    Vector4 v = Vector4.Scale (xyz, new Vector4 (1.0f / 0.95047f, 1.0f, 1.0f / 1.08883f, 1.0f));

    v.x = (v.x > 0.008856f) ? Mathf.Pow (v.x, 1.0f / 3.0f) : (7.787f * v.x + 16.0f / 116.0f);
    v.y = (v.y > 0.008856f) ? Mathf.Pow (v.y, 1.0f / 3.0f) : (7.787f * v.y + 16.0f / 116.0f);
    v.z = (v.z > 0.008856f) ? Mathf.Pow (v.z, 1.0f / 3.0f) : (7.787f * v.z + 16.0f / 116.0f);

    float L = 116.0f * v.y - 16.0f;
    float a = 500.0f * (v.x - v.y);
    float b = 200.0f * (v.y - v.z);
    return new Vector4 (a, L, b, xyz.w);
}

static Vector4 CieLabToXyz (in Vector4 lab)
{
    float L = lab.y;
    float a = lab.x;
    float b = lab.z;

    float vy = (L + 16.0f) / 116.0f;
    float vx = a / 500.0f + vy;
    float vz = vy - b / 200.0f;

    float vye3 = vy * vy * vy;
    float vxe3 = vx * vx * vx;
    float vze3 = vz * vz * vz;

    vy = (vye3 > 0.008856f) ? vye3 : ((vy - 16.0f / 116.0f) / 7.787f);
    vx = (vxe3 > 0.008856f) ? vxe3 : ((vx - 16.0f / 116.0f) / 7.787f);
    vz = (vze3 > 0.008856f) ? vze3 : ((vz - 16.0f / 116.0f) / 7.787f);

    return new Vector4 (vx * 0.95047f, vy, vz * 1.08883f, lab.w);
}

static Color XyzToLinear (in Vector4 xyz)
{
    // This could also be written as matrix-vector multiplication.
    return new Color (
        3.2408123f * xyz.x - 1.5373085f * xyz.y - 0.49858654f * xyz.z, //
        -0.969243f * xyz.x + 1.8759663f * xyz.y + 0.041555032f * xyz.z,
        0.0556384f * xyz.x - 0.20400746f * xyz.y + 1.057129f * xyz.z,
        xyz.w);
}

static Color LinearToStandard (in Color c)
{
    return new Color (
        LinearToStandardChannel (c.r),
        LinearToStandardChannel (c.g),
        LinearToStandardChannel (c.b),
        c.a);
}