Retrieve Exact Rgb Value From Touch Event In Camera Preview

I've been working on an Android app that simply needs to retrieve and display the coordinates and RGB values of a touch event on the camera preview. I'm a beginner at this programm

Solution 1:

the second example should work, the problem is that x and y are not initialized, so in method onCameraFrame, where you initialize rgb = mRgba.get(x,y), after this rgb is still null, since x and y are not initialized. Hence, your nullPointerException when you try to print it.

What I would suggest is that you just initialize x and y to -1 in the beginning:

int x=-1, y=-1;

and then in touch handler method you update x and y like so:

public boolean onTouchEvent(MotionEvent event) {
    x = (int)event.getX();
    y = (int)event.getY();
    return super.onTouchEvent(event);
}

and in the onCameraFrame method you do something like this:

publicMatonCameraFrame(CvCameraViewFrame inputFrame) {
  mRgba = inputFrame.rgba();
  if(x != -1 && y != -1) { //if this is true, you've touched something
    rgb = mRgba.get(x,y);
    touchView.setText("Touch coordinates--> " + "x: " + String.valueOf(x) 
            + " y: " + String.valueOf(y) + " \n" + "RGB values--> " + "Red: " + rgb[0]
            + " Green: " + rgb[1] + " Blue: " + rgb[2]);
    x = -1; 
    y = -1;
  }

return mRgba;
}

Hope this helps