A method of compressing image data in a display apparatus in a unit of block including a plurality of pixels includes generating a residual signal by predicting image data of a plurality of second blocks disposed in a second horizontal line using image data of a plurality of first blocks disposed in a first horizontal line, where the second horizontal line is disposed under the first horizontal line, determining whether operating discrete cosine transform (“DCT”) to the residual signal or not based on an input image, compressing the image data of the second blocks and determining compressibility of image data of a plurality of third blocks disposed in a third horizontal line disposed under the second horizontal line based on compressibility of the image data of the second blocks.