dispatchRect method
Implementation
@override
Uint8List dispatchRect(Uint8List data, int width, int height, Rect rect) {
if ((rect.left == 0 && rect.right == 0) ||
(rect.top == 0 && rect.bottom == 0)) {
return dispatch(data, width, height);
}
return grayScaleProcess[random.nextInt(grayScaleProcess.length)]
.dispatch(data, width, height, rect);
}