An encoding method, medium, and system encoding an image, with an image being encoded by generating a plurality of image slices as images of each color component of the image and encoding the image slices in parallel with each other and independently of each other. Accordingly, although an image to be encoded has a large number of color components, the image can be compressed promptly. In addition, a decoding method, medium, and system are also provided decoding an image, with a plurality of encoded image slices being included in a corresponding bitstream, which are images of each color component of the image to be restored, are decoded in parallel with each other and independently of each other so as to restore the image using the decoded image slices. Accordingly, although an image to be decoded has a large number of color components, the image can be restored promptly.