OpenCV and Android: drawContrours from a ROI at correct position in image

Question

On Android by using OpenCV I try to draw contours I got from a ROI but I am not able to draw them at the correct place at the image.

Mat resultImage= ...; // source

Rect roi = new Rect(x, y, widht, height);
Mat mat = new Mat(resultImage, roi);

Imgproc.adaptiveThreshold(mat, mat, 255, Imgproc.ADAPTIVE_THRESH_MEAN_C, Imgproc.THRESH_BINARY_INV, 15, 4);

mat.convertTo(mat, CvType.CV_32SC1);

List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
Mat hierarchy = new Mat();
Imgproc.findContours(mat, contours, hierarchy, Imgproc.RETR_FLOODFILL, Imgproc.CHAIN_APPROX_SIMPLE);

mat.release();

Imgproc.drawContours(resultImage, contours, -1, new Scalar(255,0,0), 1);

It draws the contours on the left top corner. But I need it at "x","y" where the ROI is from.

Is there a way to add a offset to any contour?

Answer 1

I got it:

Imgproc.drawContours(resultImage, contours, -1, new Scalar(255,0,0), 1, 8, hierarchy, 1, new Point(x,y));

It is able to add the offset by using the "Point-Class"