I am trying to allow the user to touch the image and then basically a cirular magnifier will show that will allow the user to better select a certain area on the image. When the user releases the touch the magnified portion will dissapear. This is used on several photo editing apps and I am trying to implement my own version of it. The code I have below does magnify a circular portion of the imageview but does not delete or clear the zoom once I release my finger. I currently set a bitmap to a canvas using canvas = new Canvas(bitMap); and then set the imageview using takenPhoto.setImageBitmap(bitMap); I am not sure if I am going about it the right way. The onTouch code is below:

zoomPos = new PointF(0,0);
        takenPhoto.setOnTouchListener(new OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                 int action = event.getAction(); 
                    switch (action) { 
                        case MotionEvent.ACTION_DOWN: 
                            zoomPos.x = event.getX();
                            zoomPos.y = event.getY();
                            matrix.reset();
                            matrix.postScale(2f, 2f, zoomPos.x, zoomPos.y);
                            shader.setLocalMatrix(matrix);
                            canvas.drawCircle(zoomPos.x, zoomPos.y, 20, shaderPaint);
                            takenPhoto.invalidate();
                            break; 
                        case MotionEvent.ACTION_MOVE: 
                            zoomPos.x = event.getX();
                            zoomPos.y = event.getY();
                            matrix.reset();
                            matrix.postScale(2f, 2f, zoomPos.x, zoomPos.y);
                            canvas.drawCircle(zoomPos.x, zoomPos.y, 20, shaderPaint);
                            takenPhoto.invalidate();
                            break; 
                        case MotionEvent.ACTION_UP:   
                            //clear zoom here?

                            break; 
                        case MotionEvent.ACTION_CANCEL: 
                            break; 
                        default: 
                            break; 
            }
                    return true; 
            } 
            });