Opencv Android Java Matrix Submatrix (roi Region Of Interest)

I've mRgba Matrix and a Rect r (something recognized in the frame) I want a sub-matrix of this part of the frame which is defined by the Rect r. when I use it like this: sub = mRgb

Solution 1:

Your code does not work as you expected because it is impossible to change number of colors in-place. You need a temporary matrix to make it work:

Mat tmp;
Imgproc.cvtColor(sub, tmp, Imgproc.COLOR_RGBA2GRAY); //make it gray
Imgproc.cvtColor(tmp, sub, Imgproc.COLOR_GRAY2RGBA); //change to rgb

Solution 2:

sub = mRgba.submat(r);

Imgproc.cvtColor(sub, sub, Imgproc.COLOR_RGBA2GRAY, 1); //make it gray
Imgproc.cvtColor(sub, sub, Imgproc.COLOR_GRAY2RGBA, 4); //change to rgb

sub.copyTo(mRgba.submat(r));

ok this seems to do the trick :) it copies the changed subpicture/matrix back in the region of the source.. (what is normally done with setROI and copyto)