Digital images are single pictures or photos that are rendered from the colors produced by dots (pixels) arranged on image planes. (see Fig. 1.1) The total number of pixels determines the degree of detail (resolution), and color intensity (pixel value) determines the brightness and color. 3 bytes(3 byte = 24 bit) x 720 x 480 = 1036800 bytes = approx. 1 Megabyte. Therefore, one TV screen image will take up an entire floppy disk. So in order to maximize the utilization of digital images, technology to describe this image using less data (encoding and compression) and technology to return the image to its original state (decoding and expansion) is essential.