Patent ID: 7720149

Claim:
An image decoding apparatus for decoding at least a first coded bit stream into which header information of the H.263 coding scheme and image coded data encoded in the H.263 coding scheme are multiplexed, or for decoding a second coded bit stream into which header information of the MPEG-4 coding scheme and image coded data encoded in the MPEG-4 coding scheme are multiplexed, the image decoding apparatus comprising: coding scheme decision means for making a decision as to whether a received coded bit stream is the first coded bit stream or the second coded bit stream in response to the first header information or to the second header information; and DC coefficient decoding means for decoding a DC coefficient in the MPEG-4 decoding scheme including a switch for switching a decoding analysis scheme of decoding a direct current component of an intra-coded DCT coefficient according to the received first coded bit stream and the received second coded bit stream, wherein when the first coded bit stream is received, the DC coefficient decoding means decodes the direct current component of the intra-coded DCT coefficient by a predetermined fixed code length.