1. A processor-readable medium storing code representing instructions configured to cause a processor to: receive a plurality of pixel values, each pixel value being associated with a pixel within a portion of a frame of a video image; using the plurality of pixel values, calculate an average pixel value for each group of pixels from a plurality of groups of pixels in the portion of the frame to determine an average altitude parameter for each group of pixels from the plurality of groups of pixels; and calculate a difference in the average altitude parameter of a group of pixels from the plurality of groups of pixels having a largest average altitude parameter and the average altitude parameter of a group of pixels from the plurality of groups of pixels having a smallest average altitude parameter to determine a degree of slope parameter for the portion of the frame.