A method of decoding image data includes operating a decoder including a decoding buffer and a decoding module, wherein the decoding module includes a plurality of decoding channels, setting a non-shared memory region and a shared memory region in the decoding buffer, restoring a plurality of frames by decoding a bitstream using the plurality of decoding channels, determining a type of each of the frames, and writing each frame to one of the non-shared memory region or the shared memory region based on the type of each frame.