In one aspect, a mobile device is provided which includes a memory configured to store an original image and an output image, a display device configured to display the output image, and an image decoder. The image decoder is configured to receive the original image from the memory, to identify blocks included in the original image that are capable of being independently decoded, to generate the output image by pre-scaling each of the identified blocks on the basis of a size of a display image, and to store the generated output image in the memory.