A timing controller includes a data grouping part that generates a plurality of grayscale groups based on input image data, each grayscale group including n×m grayscales, a grayscale classifying part that generates a plurality of grayscale patterns respectively corresponding to the grayscale groups, a grayscale in the grayscale groups being classified in the grayscale patterns as a first grayscale if the grayscale is higher than a first reference grayscale or as a second grayscale if the grayscale is lower than a second reference grayscale, a pattern comparing part that compares each grayscale pattern with a first pattern including the n×m first and second grayscales, a pattern counter that counts a number of patterns of the grayscale patterns that are substantially the same as the first pattern, and a driving mode changing part that changes a driving mode of a display panel when the number is greater than a reference number.