From an imageview touch point can you resize a MAT to get that points color?

Question

In landscape orientation, I using myImageView.setImageBitmap(myBitmap) and using an ontouch listener to getX and getY and adjust for location of myImageView (same as getRawX and getRawY). I then use bitmapToMat to build a MAT to process the image more with OpenCV. I found two resizing scenarios where the onTouch location will draw a circle exactly where I touched but at times the location will be outside the Mat and cause a NPE and fail during processing.

Scenario 1: resize(myImageView.getWidth(), myImageView.getHeight())

Scenario 2: resize(myImageView.getHeight(), myImageView.getWidth()) and

x = x(myImage.getHeight()/myImageView.getWidth())

y = y(myImage.getWidth()/myImageView.getHeight())

If I dont change the x,y I can click everywhere in image w/o the NPE but the circle drawn is nowhere near where I touched.

After processing I matToBitmap(myMAT, newBitmap) and myImageView.setImageBitmap(newBitmap) .

I am obviously missing something but is there there a simple way to get the touch location and use that location in a MAT? Any help would be awesome!

Can you share the screen shot of your application. The onTouch callback x and y coordinates are w.r.t ImageView, and if your Bitmap doesn't occupies the full ImageView then you may always get incorrect touch coordinates. — ZdaR, Jan 18 '18 at 03:13

score 2 · Answer 1 · answered Jan 22 '18 at 16:34

You have to offset the touched coordinates as the view might be bigger or smaller than the mat. Something like this should work

private Scalar getColor(View v, MotionEvent event){
    int cols = yourMat.cols();
    int rows = yourMat.rows();

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

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

  Point  touchedPoint    = new Point(x,y);

  Rect   touchedRect = new Rect();

    touchedRect.x = (x>4) ? x-4 : 0;
    touchedRect.y = (y>4) ? y-4 : 0;

    touchedRect.width = (x+4 < cols) ? x + 4 - touchedRect.x : cols - touchedRect.x;
    touchedRect.height = (y+4 < rows) ? y + 4 - touchedRect.y : rows - touchedRect.y;

    Mat touchedRegionRgba = yourMat.submat(touchedRect);

    Scalar mBlobColor = Core.mean(touchedRegionRgba);

    touchedRegionRgba.release();

    return mBlobColor;
}

From an imageview touch point can you resize a MAT to get that points color?

1 Answers1