I have a problem with putting my convexity defects on the frame. To calculate them, I modified c++ source and this is what i archived:
mConvexityDefectsMatOfInt4 = new MatOfInt4();
if(contours.size() > 0 && convexHullMatOfInt.rows() > 0)
Imgproc.convexityDefects(contours.get(0), convexHullMatOfInt, mConvexityDefectsMatOfInt4);
However, the Imgproc.drawContours(...) method requires that convexityDefects passed to it as a parameters will be ArrayList. I don't know how can I make the conversion. I had also similar problem with convex hulls, but I found out a walkaround:
convexHullMatOfInt = new MatOfInt();
convexHullPointArrayList = new ArrayList<Point>();
convexHullMatOfPoint = new MatOfPoint();
convexHullMatOfPointArrayList = new ArrayList<MatOfPoint>();
//Calculate convex hulls
if(contours.size() > 0)
{
Imgproc.convexHull( contours.get(0), convexHullMatOfInt, false );
for(int j=0; j < convexHullMatOfInt.toList().size(); j++)
convexHullPointArrayList.add(contours.get(0).toList().get(convexHullMatOfInt.toList().get(j)));
convexHullMatOfPoint.fromList(convexHullPointArrayList);
convexHullMatOfPointArrayList.add(convexHullMatOfPoint);
}
Similar solution for convexity defects is not working. Does anyone have an idea on how can I solve the problem?
How to convert from MatOfInt4() to ArrayList() to be able to draw convexity defects?
(I myself was struggling so much with convexityDefect
that I wanted to kill whoever has written the Java interface for OpenCV!)
Now the answer:
As stated in docs, MatOfInt4
is basically a 4-element integer array containing the following information:
start_index
end_index
farthest_pt_index
fixpt_depth
You can use the following to convert mConvexityDefectsMatOfInt4
to a list of integers:
List<Integer> cdList = mConvexityDefectsMatOfInt4.toList();
Now, each 4 consecutive elements in cdList
holds the info stated above:
cdList 0 : 23
cdList 1 : 30
cdList 2 : 26
cdList 3 : 18101
-----------------
cdList 4 : 30
cdList 5 : 44
cdList 6 : 33
cdList 7 : 43738
So, for example if you want to draw only the farthest point of each concavity, you can simply use the third index of each 4 elements. In this case: 26, 33, ...
Hope it helps.