Android - Template Matching

Question

I want to create an android application. Program steps are below

1. Open camera
2. Get frames
3. Select a frame by touch screen
4. Load template image under drawable folder
5. Apply template matching
6. Show result

The mat object of template image is not empty. I check it. When I run this code, I get below error message.

Code :

public void onCameraViewStarted(int width, int height) {
    mRgba = new Mat(height, width, CvType.CV_8UC4);
    temp = new Mat(height, width, CvType.CV_8UC4);
}

public boolean onTouch(View v, MotionEvent event) {
    int cols = mRgba.cols();
    int rows = mRgba.rows();

    int xOffset = (mOpenCvCameraView.getWidth() - cols) / 2;
    int yOffset = (mOpenCvCameraView.getHeight() - rows) / 2;

    int x = (int)event.getX() - xOffset;
    int y = (int)event.getY() - yOffset;

    Log.i(TAG, "Touch image coordinates: (" + x + ", " + y + ")");

    if ((x < 0) || (y < 0) || (x > cols) || (y > rows)) return false;

    mIsColorSelected = true;
    return true; // don't need subsequent touch events
}

private static Mat readInputStreamIntoMat(InputStream inputStream) throws IOException {
    // Read into byte-array
    byte[] temporaryImageInMemory = readStream(inputStream);

    // Decode into mat. Use any IMREAD_ option that describes your image appropriately
    Mat outputImage = Highgui.imdecode(new MatOfByte(temporaryImageInMemory), Highgui.IMREAD_GRAYSCALE);

    return outputImage;
}

private static byte[] readStream(InputStream stream) throws IOException {
    // Copy content of the image to byte-array
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    int nRead;
    byte[] data = new byte[16384];

    while ((nRead = stream.read(data, 0, data.length)) != -1) {
        buffer.write(data, 0, nRead);
    }

    buffer.flush();
    byte[] temporaryImageInMemory = buffer.toByteArray();
    buffer.close();
    stream.close();
    return temporaryImageInMemory;
}
public Mat onCameraFrame(CvCameraViewFrame inputFrame) {

    if(mIsColorSelected) {
   InputStream inpT = getResources().openRawResource(R.drawable.imgt);
   Mat mTemp;
        try {
            mRgba.copyTo(temp);
            mTemp = readInputStreamIntoMat(inpT);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        // / Create the result matrix
        int result_cols = temp.cols() - mTemp.cols() + 1;
        int result_rows = temp.rows() - mTemp.rows() + 1;
        Mat result = new Mat(result_rows, result_cols, CvType.CV_32FC1);
        int match_method = 4;
        // / Do the Matching and Normalize
        Imgproc.matchTemplate(temp, mTemp, result, match_method);
          Core.normalize(result, result, 0, 1, Core.NORM_MINMAX, -1, new Mat());
     /*
         Localizing the best match with minMaxLoc
        MinMaxLocResult mmr = Core.minMaxLoc(result);

        Point matchLoc;
        if (match_method == Imgproc.TM_SQDIFF || match_method == Imgproc.TM_SQDIFF_NORMED) {
            matchLoc = mmr.minLoc;
        } else {
            matchLoc = mmr.maxLoc;
        }/*
        // / Show me what you got
        Core.rectangle(temp, matchLoc, new Point(matchLoc.x + mTemp.cols(),
                matchLoc.y + mTemp.rows()), new Scalar(0, 255, 0));*/
        return temp;
    }
    else {
        mRgba = inputFrame.rgba();
    }

    return mRgba;
}

Answer 1

For template matching , both source image and template image must be of same data type( 1 ). Here your template image( mTemp ) is a gray scale image and source image( mRgba / temp ) is a color image with alpha channel.

So, lets change both source and template images to be gray scale images

temp = new Mat(height, width, CvType.CV_8UC1);

and replace mRgba.copyTo(temp) with

Imgproc.cvtColor(mRgba, temp, Imgproc.COLOR_RGBA2GRAY);