Android: Draw contours arround points detected by MSER
I'm trying to draw countours to indicate the points detected by MSER in a bitmap.
I can detect the points with FeatureDectector.detect()
but it returns them as MatOfKeyPoint.
Now I want to dray the contour of these points using Imgproc.drawContours()
, but this function receives the points as a List<MatOfPoint>
.
I have tried to convert MatOfKeyPoint to List<MatOfPoint>
, then use drawContours()
.
This is what I have tested:
private void processBitmap(Bitmap bmp){
Mat mat = new Mat(bmp.getWidth(), bmp.getHeight(),
CvType.CV_16S, new Scalar(4));
Utils.bitmapToMat(bmp, mat);
Imgproc.cvtColor(mat, mat, Imgproc.COLOR_RGB2GRAY, 4);
FeatureDetector fd = FeatureDetector.create(FeatureDetector.MSER);
MatOfKeyPoint mokp = new MatOfKeyPoint();
fd.detect(mat, mokp);
KeyPoint[] kps = mokp.toArray();
List<MatOfPoint> mops = new ArrayList<MatOfPoint>(kps.length);
for(int i = 0; i < kps.length; i++)
mops.set(i, new MatOfPoint(kps[i].pt));
Scalar s = new Scalar(0);
Imgproc.drawContours(mat, mops, 1, s);
Utils.matToBitmap(mat, bmp);
}
In this case, there is no exceptions, but drawContours()
does nothing.
I have tested this too:
import org.opencv.core.Point;
[...]
private void processBitmap(Bitmap bmp){
Mat mat = new Mat(bmp.getWidth(), bmp.getHeight(),
CvType.CV_16S, new Scalar(4));
Utils.bitmapToMat(bmp, mat);
Imgproc.cvtColor(mat, mat, Imgproc.COLOR_RGB2GRAY, 4);
FeatureDetector fd = FeatureDetector.create(FeatureDetector.MSER);
MatOfKeyPoint mokp = new MatOfKeyPoint();
fd.detect(mat, mokp);
KeyPoint[] kps = mokp.toArray();
Scalar s = new Scalar(0); //color black
Point[] points = new Point[kps.length]; //
for(int i = 0; i < points.length; i++)
points[i] = kps[i].pt;
MatOfPoint mop = new MatOfPoint();
mop.fromArray(points);
List<MatOfPoint> lmop = new ArrayList<MatOfPoint>();
lmop.add(mop);
Imgproc.drawContours(mat, lmop, 5, s);
Utils.matToBitmap(mat, bmp);
}
In this case there is an exception:
OpenCV Error: Assertion failed (0 <= contourIdx && contourIdx < (int)last
I have read the documentation of OpenCV for java here:
But the example is only with findContours()
.
I have read that MatOfPoint is only a way used by OpenCV to avoid to copy points between native part and java part,
(See: http://www.answers.opencv.org/questio...)
so that, I assume that the List<MatOfPoint>
must have only 1 component due to MatOfPoint contains all points I need, is this correct?
How can I convert the MatOfKeyPoint
in List<MatOfPoint>
properly?