1. A method for detecting a constant region of an image frame, comprising: determining, with at least one processor, that a first region of pixels in an image analysis window at a first position is a constant region; in response to determining that the first region is a constant region: determining, with the at least one processor, that a second region in the image analysis window at a second position is a constant region by analyzing a number of pixels in the second region that is less than a total number of pixels in the second region.