Stretch all of the image rows in order to make them of constant length

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Hi, I have the left side image and I want to stretch the rows in order to obtain the right side image.

APPROACH 1:

This code (from here), gives me the contours.

vector< vector<Point> > contours;
contours.push_back(contour);

// you could also reuse img1 here
Mat mask = Mat::zeros(poseNormImg.rows, poseNormImg.cols, CV_8UC1);

// CV_FILLED fills the connected components found
drawContours(mask, contours, -1, Scalar(255), CV_FILLED);

// let's create a new image now
Mat crop(poseNormImg.rows, poseNormImg.cols, CV_8UC3);

// set background to green
crop.setTo(Scalar(255,255,0));

// and copy the magic apple
poseNormImg.copyTo(crop, mask);

imshow("cropped", crop);

How can I stretch the image from the contours, since it is a polygon with 10 points and and not a rectangle?

APPROACH 2:

Based on this question, I implemented this function , witch allow me to stretch a rectangle.

/**
 * http://stackoverflow.com/questions/7838487/executing-cvwarpperspective-for-a-fake-deskewing-on-a-set-of-cvpoint
 */
Mat deskewing(Mat src, Point pt1, Point pt2, Point pt3, Point pt4)
{
    vector<Point> not_a_rect_shape;
    not_a_rect_shape.push_back(pt1);
    not_a_rect_shape.push_back(pt2);
    not_a_rect_shape.push_back(pt3);
    not_a_rect_shape.push_back(pt4);

    // Assemble a rotated rectangle out of that info
    RotatedRect box = minAreaRect(cv::Mat(not_a_rect_shape));
    std::cout << "Rotated box set to (" << box.boundingRect().x << "," << box.boundingRect().y << ") " << box.size.width << "x" << box.size.height << std::endl;

    Point2f pts[4];

    box.points(pts);

    cv::Point2f src_vertices[3];
    src_vertices[0] = pts[0];
    src_vertices[1] = pts[1];
    src_vertices[2] = pts[3];

    Point2f dst_vertices[4];
    dst_vertices[0] = Point(0, 0);
    dst_vertices[1] = Point(box.boundingRect().width-1, 0); // Bug was: had mistakenly switched these 2 parameters
    dst_vertices[2] = Point(0, box.boundingRect().height-1);
    dst_vertices[3] = Point(box.boundingRect().width-1, box.boundingRect().height-1);


    Mat warpAffineMatrix = getAffineTransform(src_vertices, dst_vertices);

    cv::Mat rotated;
    cv::Size size(src.cols/2/*box.boundingRect().width*/, box.boundingRect().height);
    warpAffine(src, rotated, warpAffineMatrix, size, INTER_LINEAR, BORDER_CONSTANT);

    return rotated;
}

Since I was not able to stretch the entire polygon sub matrix, I thought of decomposing the polygon in to rectangles, stretching those areas and then sum them.

Using this approach I have two problems: the rectangle area is re sized to min area and rotated.

Is this the correct approach or is there another way?

Thank you