Clear (not crop) the non-ROI part of image in OpenCV

Question

I have a Mat and I successfully cropped the ROI (lower-half part of image). But the problem is, I want the upper-half part of image to be blank(white in color) and the cropped image in the lower-half. Here is my existing code -

Rect imgROI(0, temporaryImage.size().height - (temporaryImage.size().height / 2), temporaryImage.size().width, temporaryImage.size().height / 2);
Mat croppedImage = temporaryImage(imgROI);

Any ideas on how to do that?

Answer 1

Just set ROI of upper-half to zero:

  cv::Rect blankRoi(0, 0, temporaryImage.size().width, temporaryImage.size().height / 2);
  temporaryImage(blankRoi).setTo(cv::Scalar(0));