The function of buildOpticalFlowPyramid and calcOpticalFlowPyrLK in OpenCV-2.4.8-android-sdk is:



public static int buildOpticalFlowPyramid(Mat img, List<Mat> pyramid, Size winSize, int maxLevel)



public static void calcOpticalFlowPyrLK(Mat prevImg, Mat nextImg, MatOfPoint2f prevPts, MatOfPoint2f nextPts, MatOfByte status, MatOfFloat err, Size winSize, int maxLevel, TermCriteria criteria, int flags, double minEigThreshold)



If I just use the image as the input of calcOpticalFlowPyrLK, not using pyramid, it works well. But If I use buildOpticalFlowPyramid to bulid a pyramid as input of calcOpticalFlowPyrLK. The List<Mat> pyramid is not applicable for Mat prevImg.



If I declare the pyramid as vector<Mat>, buildOpticalFlowPyramid works well, but the app will be forced to stop whenever call calcOpticalFlowPyrLK.



Here is parts of the code.

<pre>



MatOfByte status = new MatOfByte();

int maxlevel=2;



Mat prev = new Mat(mRgba.size(),CvType.CV_8UC1);

Mat curr = new Mat(mRgba.size(),CvType.CV_8UC1);

List<Mat> pyramid1= new ArrayList<Mat>(maxlevel);

List<Mat> pyramid2= new ArrayList<Mat>(maxlevel);



Mat pyramid3 = new Mat();

Mat pyramid4 = new Mat();




MatOfPoint2f featurestracked = new MatOfPoint2f();

MatOfFloat err = new MatOfFloat();



int i,count;

TermCriteria optical_flow_termination_criteria =new TermCriteria();



optical_flow_termination_criteria.epsilon =.03;

optical_flow_termination_criteria.maxCount = 20;

Size winSize = new Size(21,21);





Imgproc.cvtColor(hp.TrackingFrame, prev, Imgproc.COLOR_RGBA2GRAY,0);



Imgproc.cvtColor(mRgba, curr, Imgproc.COLOR_RGBA2GRAY,0);



//Build pyramid

int level1= Video.buildOpticalFlowPyramid(prev, pyramid1, winSize, maxlevel);


int level2 = Video.buildOpticalFlowPyramid(curr, pyramid2, winSize, maxlevel);





pyramid3 = Converters.vector_Mat_to_Mat(pyramid1);

pyramid4 = Converters.vector_Mat_to_Mat(pyramid2);




MatOfPoint2f features_next2f = new MatOfPoint2f(hp.features_next.toArray());



Video.calcOpticalFlowPyrLK(pyramid3, pyramid4,features_next2f,featurestracked,status,err, winSize,maxlevel,optical_flow_termination_criteria, 0, 0.001);
</pre>