Pixels of a bitmap when touched turn transparent in java android

I have a frame layout with two overlapping bitmaps as imageviews and on touch, the touched pixels only should turn transparent.But instead the entire image turns transparent.

I did refer a similar link Making Overlaid image transparent on touch in Android? But it was of no help.The code for the touchEvent is below.

@Override public boolean onTouchEvent(MotionEventevent){ startX = (int)event . getX(); startY = (int)event . getY(); switch (event . getAction()) { case MotionEvent . ACTION_DOWN: return true; case MotionEvent . ACTION_MOVE: try { newOverlayBitmap = Bitmap . createBitmap(bmp . getWidth() , bmp . getHeight() , bmp . getConfig()); for (inti = 0; i < bmp . getWidth(); i++) { for (intj = 0; j < bmp . getHeight(); j++) { if (i == startX && j == startY) { p = bmp . getPixel(i, j); r = Color . red(p); g = Color . green(p); b = Color . blue(p); alpha = Color . alpha(p); alpha = 256 - alpha;//alpha=1 newOverlayBitmap . setPixel(i, j, Color . argb(alpha, r, g, b)); } } } img . setImageBitmap(newOverlayBitmap); //sets the changed overlay on the imageview } catch(Exceptione) { e . printStackTrace(); } break; case MotionEvent . ACTION_UP: break; default: a = false; } a = true; super . onTouchEvent(event); return a; }