OpenCV stereo variation map.

- (void) computeStereoVarMapWithImageLeft:(CGImageRef)leftImage
                               imageRight:(CGImageRef)rightImage
                           minDisparities:(NSUInteger)minDisparities
                           maxDisparities:(NSUInteger)maxDisparities
                               iterations:(NSUInteger)iterations
                                    polyN:(NSUInteger)polyN
                                polySigma:(double)polySigma
                                       fi:(double)fi
                                   lambda:(double)lambda
{
    /**
     * Convert the CGImageRef to cv::Mat
     */
    cv::Mat left = [self CVMatWithCGImage:leftImage];
    cv::Mat right = [self CVMatWithCGImage:rightImage];

    /**
     * Initialization of cv::StereoVar
     */
    cv::StereoVar var;

    // Hard-coded
    var.levels = 3;
    var.pyrScale = 0.25;

    /**
     * Stereo Variation parameters
     */
    var.nIt = (int)iterations;
    var.minDisp = -(int)minDisparities;
    var.maxDisp = (int)maxDisparities;
    var.poly_n = (int)polyN;
    var.poly_sigma = polySigma;
    var.fi = fi;
    var.lambda = lambda;
    var.penalization =  cv::StereoVar::PENALIZATION_TICHONOV;
    var.cycle = cv::StereoVar::CYCLE_V;
    var.flags = cv::StereoVar::USE_SMART_ID | cv::StereoVar::USE_MEDIAN_FILTERING;


    /**
     * Need to downscale the original images to get a decent framerate.
     */
    cv::resize(left, left, cv::Size(), 0.25, 0.25, cv::INTER_CUBIC);
    cv::resize(right, right, cv::Size(), 0.25, 0.25, cv::INTER_CUBIC);

    /**
     * Initialize the disparity map cv::Mat.
     */
    cv::Mat disparity8 = cv::Mat(left.rows, left.cols, CV_8UC1);

    /**
     * Compute the disparity map.
     */
    var(left, right, disparity8);

    /**
     * Upscale the resulting disparity map.
     */
    cv::resize(disparity8, disparity8, cv::Size(640, 480), 0, 0, cv::INTER_CUBIC);

    /**
     * Convert it to CGImageRef in order to be able to get a QC provider from the plug-ins.
     */
    _disparityImage = [self CGImageRefWith:disparity8];

}