1. A method of processing image data, the method comprising: loading at least a portion of each of two horizontal rows of pixel values into memory, each horizontal row of pixel values including a plurality of N pixel values, each pixel value in a row corresponding to one of N different columns of pixel values; designating a second row of pixel values to be a current set of pixel values; comparing a pixel value of the first column of the current row of pixel values to a pixel value of the first column of the immediately preceding row of pixel value to determine if the pixel value of the first column of the current row is different from the pixel value of the first column of the immediately preceding row; if it is determined that the pixel value of the first column of the current row of pixel values is different from the pixel value of the first column of the immediately preceding row, updating a set of detected pixel value change location information indicating, for the first column, that a change in pixel values was detected in the first column at the current row; comparing a pixel value of the second column of the current row of pixel values to a pixel value of the second column of the immediately preceding row of pixel value to determine if the pixel value of the second column of the current row is different from the pixel value of the second column of the immediately preceding row; if it is determined that the pixel value of the second column of the current row of pixel values is different from the pixel value of the second column of the immediately preceding row, updating a set of detected pixel value change location information indicating, for the second column, that a change in pixel values was detected in the second column at the current row; and generating vertical pixel value run length information for the first column of pixel values from the set of detected pixel value change location information corresponding to the first column, wherein the vertical pixel value run length information includes information indicating the number of consecutive rows a pixel value remains unchanged in the vertical column of pixel values to which the vertical pixel run length information corresponds; and wherein generating the vertical pixel value run length information includes subtracting a number of a preceding row in which a change was detected from a number of a row in which a change was detected, said difference indicating the number of rows for which the pixel value remained unchanged.