1. An image processor that is configured to: determine that an entire area of an image analysis window at a previous position of an image frame is a constant region; and in response to determining that the entire area of the image analysis window at the previous position is a constant region, analyze, at a current position of the image frame, a number of pixels in the image analysis window that is less than a total number of pixels in the image analysis window; and determine that an entire area of the image analysis window at the current position is a constant region based on the analysis of the number of pixels in the image analysis window that is less than the total number of pixels at the current position.