Question

in opencv there is no difference between an image and a ROI of an image. a cv::Mat object can be either:

cv::Mat img = cv::imread(fileName);
cv::Mat imgROI(img,cv::Rect(1,2,30,40));

My question is how can I extract the original ROI coordinates in the original image, i.e. some function that preforms the following:

cv::Rect originalROIcoords  = roiLocationInOriginalImg(imgROI);
cv::Rect originalROIcoords2 = roiLocationInOriginalImg(img );

originalROIcoords should be (1,2,30,40), while originalROIcoords2 should be (0,0,w,h), where w and h are the original image width and height respectively.

Thanks.

Ohad

Answer 1

To know the coordinates of a submatrix in the original matrix, you can use the function Mat::locateROI

// locates matrix header within a parent matrix
void locateROI( Size& wholeSize, Point& ofs ) const;