Low FPS when using CascadeClassifier in Android

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I'm new to OpenCV and I've loaded the sample face detection app onto my Android device (Samsung Galaxy Nexus) and it works brilliantly, with a FPS around 20-25 FPS (depending on lighting conditions).

However, when I go to make my own code (which is highly based upon the sample code), the frame rate drops considerably, and now I'm only getting around 1-2 FPS.

I'm following the basic skeleton of the sample application, and the important work is done in the onCameraFrame method, which is as follows:

@Override
public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
    // this method recieves the input frame from the camera BEFORE it is drawn on the
    // screen of the device. The face detection happens here.

    rgba = inputFrame.rgba();
    gray = inputFrame.gray();
    MatOfRect faces = new MatOfRect(); //dense for each face
    if (javaDetector != null) {
        javaDetector.detectMultiScale(gray, faces, 1.1, 2, 2, new Size(0, 0.2f), new Size());
    }

    Rect[] arrayFaces = faces.toArray();
    for (int i = 0; i < arrayFaces.length; i++) {
        Core.rectangle(rgba, arrayFaces[i].tl(), arrayFaces[i].br(), rectangleColor, rectangleColor, 3);
    }
    return rgba;
}

The code that I have to load the library (in the BaseLoaderCallback method) is here:

private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
    @Override
    public void onManagerConnected(int status) {
        switch (status) {
            case LoaderCallbackInterface.SUCCESS:
            {
                File classifierDir = getDir("cascade", Context.MODE_PRIVATE);
                try {
                    InputStream is = getResources().openRawResource(R.raw.haarcascade_frontalface_alt);
                    File classifierFile = new File(classifierDir, "haarcascade_frontalface_alt.xml");
                    FileOutputStream os = new FileOutputStream(classifierFile);

                    byte[] buffer = new byte[4096];
                    int bytesRead;
                    while ((bytesRead = is.read(buffer)) != -1) {
                        os.write(buffer, 0, bytesRead);
                    }
                    is.close();
                    os.close();

                    javaDetector = new CascadeClassifier(classifierFile.getAbsolutePath());
                    if (javaDetector.empty()) {
                        throw new FileNotFoundException();
                    }
                    classifierDir.delete();
                } catch (FileNotFoundException ex) {
                    Log.e(TAG, "Unable to load facial definitions");
                } catch (IOException iex) {
                    Log.e(TAG, "Unable to open facial definitions file");
                }
                mOpenCvCameraView.enableView();
            } break;
            default:
            {
                super.onManagerConnected(status);
            } break;
        }
    }
};

Which is essentially the same as the sample application. Is there a reason why that my version is running so slowly?