Encoding and decoding method for enhancing depth resolution of image and print system using the same

An encoding and decoding method for improving gradation resolution of images and a printing system using the method are provided to perform encoding and decoding operations according to whether an image has an edge to thereby enhance gradation resolution of the image and reduce a time required to transmit print data. An encoding method of a host device includes a step of detecting an edge image from a gray image(S810), a step of dividing the detected edge image into a plurality of unit blocks(S820) and determining whether each unit block has an edge region(S830), and a step of applying an encoding method corresponding to the determination result to convert the gray image into binary data(S840).