An image signal modifying device includes a pixel, a memory which stores compressed information in which a three-dimensional (“3-D”) lookup table is coded, an image signal modifying unit which decodes the compressed information to generate a restored 3-D lookup table and generates a modified signal based on a first image signal of a first frame, a second image signal of a second frame, a third image signal of a third frame and the restored 3-D lookup table, and a data driver which converts the modified signal into the data voltage and supplies the data voltage to the pixel.