Move area of an image to the center using OpenCV - c++

Question

I'm trying to move a region of an image to the center, I succeeded in getting its contour and I know how to place this in the center.
But what I want is to move the pixels that are inside the contour (yellow with black) at the center and not just the contour (which is pink by CV_FILLED).
Image:
Code:
//Then segment the image. save in Mat crop
// ---- Center image -----
// pos : contour interest
RotatedRect rr = fitEllipse(contours[pos]);
vector<Point>&contour = contours[pos];
//http://stackoverflow.com/a/29467236/4595387
//difference between the centre of the image and centre of the contour
Point center = Point( crop.cols/2, crop.rows/2 );
int nX = center.x - rr.center.x;
int nY = center.y - rr.center.y;
for (size_t i=0; i< contour.size(); i++)
{
contour[i].x += nX;
contour[i].y += nY;
}
cout << "x: " << rr.center.x;
cout << "y: " << rr.center.y;
//color = Scalar(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255));
//contour of the image to the center.
cv::drawContours(crop, contours, pos, color, CV_FILLED);
imshow("In",imagen_src);
imshow("Out",crop);

Answer 1

You need basically to play around with copyTo with a mask. The steps are commented in the code. If you need a different background color, just change backgroundColor in the code below.
Code:
#include <opencv2\opencv.hpp>
using namespace cv;
int main()
{
// Read image
Mat3b img = imread("path_to_image");
// Convert to hsv
Mat3b hsv;
cvtColor(img, hsv, COLOR_BGR2HSV);
// Threshold on yellow color (in hsv space)
Mat1b maskOnYellow;
inRange(hsv, Scalar(20, 100, 100), Scalar(40, 255, 255), maskOnYellow);
// Find contours of yellow item
vector<vector<Point>> contours;
findContours(maskOnYellow.clone(), contours, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);
// Create a mask as a filled contour
Mat1b mask(img.rows, img.cols, uchar(0));
drawContours(mask, contours, 0, Scalar(255), CV_FILLED);
// Get the bounding box of the item
Rect box = boundingRect(contours[0]);
// Get the roi in the input image according to the mask
Mat3b item(img(box));
// Create a black image (same size as the yellow item and same background bolor as result image)
// to copy the result of the segmentation
Vec3b backgroundColor(0,0,0); // black
Mat3b segmentedItem(item.rows, item.cols, backgroundColor);
// Copy only the masked part
item.copyTo(segmentedItem, mask(box));
// Compute the center of the image
Point center(img.cols / 2, img.rows / 2);
// Create a result image
Mat3b res(img.rows, img.cols, backgroundColor);
// Compute the rectangle centered in the image, same size as box
Rect centerBox(center.x - box.width/2, center.y - box.height/2, box.width, box.height);
// Put the segmented item in the center of the result image
segmentedItem.copyTo(res(centerBox));
imshow("Result", res);
waitKey();
return 0;
}
Input:
Result: