void RGB2LAB4Pix(Vec3b* dst, Vec3b* src)
{
    //                                RGB —> XYZ                                //
    double var_R = ( (double)src->val[2] / 255 );       //R from 0 to 255
    double var_G = ( (double)src->val[1] / 255 ) ;      //G from 0 to 255
    double var_B = ( (double)src->val[0] / 255 ) ;      //B from 0 to 255

    if ( var_R > 0.04045 )
        var_R = pow(( ( var_R + 0.055 ) / 1.055 ), 2.4);
    else
        var_R = var_R / 12.92;

    if ( var_G > 0.04045 )
        var_G = pow(( ( var_G + 0.055 ) / 1.055 ), 2.4);
    else
        var_G = var_G / 12.92;

    if ( var_B > 0.04045 )
        var_B = pow(( ( var_B + 0.055 ) / 1.055 ), 2.4);
    else
        var_B = var_B / 12.92;

    var_R = var_R * 100;
    var_G = var_G * 100;
    var_B = var_B * 100;

    //Observer. = 2°, Illuminant = D65
    double X = var_R * 0.4124 + var_G * 0.3576 + var_B * 0.1805;
    double Y = var_R * 0.2126 + var_G * 0.7152 + var_B * 0.0722;
    double Z = var_R * 0.0193 + var_G * 0.1192 + var_B * 0.9505;

    //                             XYZ —> CIE-L*ab                             //

    double var_X = X / 95.047;          //ref_X =  95.047   Observer= 2°, Illuminant= D65
    double var_Y = Y / 100.000;          //ref_Y = 100.000
    double var_Z = Z / 108.883;          //ref_Z = 108.883

    if ( var_X > 0.008856 )
        var_X = pow(var_X, double(0.333333));
    else
        var_X = ( 7.787 * var_X ) + ( 16 / 116 );

    if ( var_Y > 0.008856 )
        var_Y = pow(var_Y, double(0.333333));
    else
        var_Y = ( 7.787 * var_Y ) + ( 16 / 116 );

    if ( var_Z > 0.008856 )
        var_Z = pow(var_Z, double(0.333333));
    else
        var_Z = ( 7.787 * var_Z ) + ( 16 / 116 );

    double CIEL = ( 116 * var_Y ) - 16;
    double CIEa = 500 * ( var_X - var_Y );
    double CIEb = 200 * ( var_Y - var_Z );

    dst->val[2] = (uchar)CIEL;
    dst->val[1] = (uchar)CIEa;
    dst->val[0] = (uchar)CIEb;
}
void TaskG()
{
    Mat Image = imread("lena.jpg");
    Mat ImageLab;
    Mat ImageLabCV;
    Image.copyTo(ImageLab);
    cvtColor(Image, ImageLabCV, CV_RGB2Lab);
    imwrite("LenaLabCV.jpg", ImageLabCV);

    //Попиксельно переводим RGB -> LAB
    for(int y = 0; y < Image.rows; ++y)
    {
        for(int x = 0; x < Image.cols; ++x)
        {
            RGB2LAB4Pix(&ImageLab.at<Vec3b>(y, x), &Image.at<Vec3b>(y, x));
        }
    }

    Mat LabDifference;
    LabDifference = abs(ImageLabCV - ImageLab);
    imwrite("LenaLabDifference.jpg", LabDifference);
}