CODEWITHSUNDEEP
javaandroidopencvfeature-detection
VassilisCN
VassilisCN

Reputation: 38

Android Opencv Why HOG descriptors are always zero?

I am stack with this problem for a couple of days. I want to make an android app that takes a picture and extracts HOG features of that image for future processing. The problem is that the code below always returns the HOG descriptors with rezo values.

@Override
public void onPictureTaken(byte[] data, Camera camera) {
    Log.i(TAG, "Saving a bitmap to file");
    // The camera preview was automatically stopped. Start it again.
    mCamera.startPreview();
    mCamera.setPreviewCallback(this);
    this.disableView();
    Bitmap bitmapPicture = BitmapFactory.decodeByteArray(data, 0, data.length);
    myImage = new Mat(bitmapPicture.getWidth(), bitmapPicture.getHeight(), CvType.CV_8UC1);
    Utils.bitmapToMat(bitmapPicture, myImage);
    Bitmap bm = Bitmap.createBitmap(myImage.cols(), myImage.rows(),Bitmap.Config.ARGB_8888);
    Utils.matToBitmap(myImage.clone(), bm);
    // find the imageview and draw it!
    ImageView iv = (ImageView) getRootView().findViewById(R.id.imageView);
    this.setVisibility(SurfaceView.GONE);
    iv.setVisibility(ImageView.VISIBLE);

    Mat forHOGim = new Mat();
    org.opencv.core.Size sz = new org.opencv.core.Size(64,128);
    Imgproc.resize( myImage, myImage, sz );
    Imgproc.cvtColor(myImage,forHOGim,Imgproc.COLOR_RGB2GRAY);
    //forHOGim = myImage.clone();
    MatOfFloat descriptors = new MatOfFloat(); //an empty vector of descriptors
    org.opencv.core.Size winStride = new org.opencv.core.Size(64/2,128/2); //50% overlap in the sliding window
    org.opencv.core.Size padding = new org.opencv.core.Size(0,0); //no padding around the image
    MatOfPoint locations = new MatOfPoint(); ////an empty vector of locations, so perform full search
    //HOGDescriptor hog = new HOGDescriptor();
    HOGDescriptor hog = new HOGDescriptor(sz,new org.opencv.core.Size(16,16),new org.opencv.core.Size(8,8),new org.opencv.core.Size(8,8),9);
    Log.i(TAG,"Constructed");
    hog.compute(forHOGim , descriptors, new org.opencv.core.Size(16,16), padding, locations);
    Log.i(TAG,"Computed");
    Log.i(TAG,String.valueOf(hog.getDescriptorSize())+" "+descriptors.size());
    Log.i(TAG,String.valueOf(descriptors.get(12,0)[0]));
    double dd=0.0;
    for (int i=0;i<3780;i++){
        if (descriptors.get(i,0)[0]!=dd) Log.i(TAG,"NOT ZERO");
    }

    Bitmap bm2 = Bitmap.createBitmap(forHOGim.cols(), forHOGim.rows(),Bitmap.Config.ARGB_8888);
    Utils.matToBitmap(forHOGim,bm2);
    iv.setImageBitmap(bm2);
}

So in the logcat I never get the NOT ZERO message. The problem is that whatever changes I do to this code I always have zeros in the descriptors MatOfFloat... And the strange part is, if I uncomment the HOGDescriptor hog = new HOGDescriptor(); and use that one instead of the one I am using now, my application crashes... The rest of the code runs fine, the picture is always taken and displayed on my image view as I expect.

Any help will be appreciated. Thanks in advance.

Upvotes: 0

Views: 711

Answers (1)

VassilisCN
VassilisCN

Reputation: 38

The problem was inside the library. When I executed the same code with OpenCV 2.4.13 for Linux and not for Android, the code worked great as expected. So I hope they will fix any problems with the HOGDescriptor for OpenCV4Android.

Upvotes: 1

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