The disclosed image processing device receiving image data comprises a first encoder, a second encoder and an encoding switch. The first encoder generates first data by encoding the image data according to a predetermined method. The second encoder generates second data by encoding the image data according to an encoding pattern table. The encoding pattern table is set up in accordance with the first data. The encoding switch determines to output either the first data or the second data as an encoded result and generates a mark value for indicating the encoded result.