Android Optical Flow with opencv

Im trying to implement optical flow in android using openCV http://code.google.com/p/android-opencv/. Basicly i want to build something like this http://www.youtube.com/watch?v=P_Sjn67jIJY . Anyway because im new to android development can anyone guide somewhere in order to build something like the one on the video? Ive already insta开发者_JS百科lled opencv port to android and build the cvcamera example successfully using eclipse. Thanks, Thanos

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See this Stanford OpenCV optical flow link. Things should work essentially the same way except the calls may be slightly different due to 1.x vs. 2.x's C vs C++ API issues.

Just edit the CVCamera example and it should be quick. I made a real-time face detection app within about an hour of getting CVCamera to work.

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Visit http://opencv.willowgarage.com/wiki/Android2.3.0 , OpenCV 2.3.0 Release Candidate has a good support for Android. There is optical flow inside it.. used it

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Although I am also trying to do the same, there seems to be more support for optical flow in OpenCV4Android now. Look at the APIs in org.opencv.video OpenCV Java documentation I see calcOpticalFlowPyrLK and calcOpticalFlowFarneback. I was able to get calcOpticalFlowFarneback to work (though the results did not seem that great, possibly need to tweak the parameters) calcOpticalFlowPyrLK is proving to be tricky. I cant seem to convert the keypoints returned by FeatureDetector class (MatOfKeyPoint) to points needed by calcOpticalFlowFarneback (MatOfPoint2f) other thread

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This code will help you get the optical vectors. And it will track them

@Override public Mat onCameraFrame(CvCameraViewFrame inputFrame) {

    mRgba = inputFrame.rgba();
    if (mMOP2fptsPrev.rows() == 0) {

        //Log.d("Baz", "First time opflow");
        // first time through the loop so we need prev and this mats
        // plus prev points
        // get this mat
        Imgproc.cvtColor(mRgba, matOpFlowThis, Imgproc.COLOR_RGBA2GRAY);

        // copy that to prev mat
        matOpFlowThis.copyTo(matOpFlowPrev);

        // get prev corners
        Imgproc.goodFeaturesToTrack(matOpFlowPrev, MOPcorners, iGFFTMax, 0.05, 20);
        mMOP2fptsPrev.fromArray(MOPcorners.toArray());

        // get safe copy of this corners
        mMOP2fptsPrev.copyTo(mMOP2fptsSafe);
        }
    else
        {
        //Log.d("Baz", "Opflow");
        // we've been through before so
        // this mat is valid. Copy it to prev mat
        matOpFlowThis.copyTo(matOpFlowPrev);

        // get this mat
        Imgproc.cvtColor(mRgba, matOpFlowThis, Imgproc.COLOR_RGBA2GRAY);

        // get the corners for this mat
        Imgproc.goodFeaturesToTrack(matOpFlowThis, MOPcorners, iGFFTMax, 0.05, 20);
        mMOP2fptsThis.fromArray(MOPcorners.toArray());

        // retrieve the corners from the prev mat
        // (saves calculating them again)
        mMOP2fptsSafe.copyTo(mMOP2fptsPrev);

        // and save this corners for next time through

        mMOP2fptsThis.copyTo(mMOP2fptsSafe);
        }


    /*
    Parameters:
        prevImg first 8-bit input image
        nextImg second input image
        prevPts vector of 2D points for which the flow needs to be found; point coordinates must be single-precision floating-point numbers.
        nextPts output vector of 2D points (with single-precision floating-point coordinates) containing the calculated new positions of input features in the second image; when OPTFLOW_USE_INITIAL_FLOW flag is passed, the vector must have the same size as in the input.
        status output status vector (of unsigned chars); each element of the vector is set to 1 if the flow for the corresponding features has been found, otherwise, it is set to 0.
        err output vector of errors; each element of the vector is set to an error for the corresponding feature, type of the error measure can be set in flags parameter; if the flow wasn't found then the error is not defined (use the status parameter to find such cases).
    */
    Video.calcOpticalFlowPyrLK(matOpFlowPrev, matOpFlowThis, mMOP2fptsPrev, mMOP2fptsThis, mMOBStatus, mMOFerr);

    cornersPrev = mMOP2fptsPrev.toList();
    cornersThis = mMOP2fptsThis.toList();
    byteStatus = mMOBStatus.toList();

    y = byteStatus.size() - 1;

    for (x = 0; x < y; x++) {
        if (byteStatus.get(x) == 1) {
            pt = cornersThis.get(x);
            pt2 = cornersPrev.get(x);

            Core.circle(mRgba, pt, 5, colorRed, iLineThickness - 1);

            Core.line(mRgba, pt, pt2, colorRed, iLineThickness);
            }
        }

return mRgba;

    }