Recently, the JVT (Joint Video Team) has standardized the H.264 (ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) Recommendation H.264|ISO (International Organization for Standardization)/IEC (International Electrotechnical Commission) 14496-10 AVC (Advanced Video Coding)) coding method as a highly efficient video coding method. In H.264, image data is handled as digital data as in the case of JPEG (Joint Photographic Experts Group), which is known as a still image coding method, and of MPEG (Moving Picture Experts Group)-2 or MPEG-4 (version 2) which are known as video coding methods.
Furthermore, particularly in the video coding method, image data is compressed using hybrid coding to reduce redundant information between frames (i.e., in the temporal direction) and redundant information of pixels within a frame (i.e., in the spatial direction) for the purpose of highly efficient information transmission and storage. In the hybrid coding, a technique, referred to as entropy coding, for performing variable-length coding using information deviation is employed together with orthogonal transformation, such as discrete cosine transform, and motion compensation.
Regarding the entropy coding employed in H.264, CAVLC (Context-Based Adaptive Variable Length Coding) that employs Huffman coding and CABAC (Context-Based Adaptive Binary Arithmetic Coding) that employs arithmetic coding are defined according to profile types. More specifically, CAVLC is selected in a baseline profile constituted by less complex coding tools for communication applications. On the other hand, CABAC is selected in main and extended profiles that focus on coding efficiency.
Japanese Patent Laid-Open Nos. 11-103257 and 2005-130099 disclose techniques for realizing CABAC by hardware. In these techniques, generation of addresses to be supplied to a context memory that holds status data and an arithmetic coding operation are performed as pipeline processing, whereby arithmetic coding of symbol data is performed during each clock cycle without delay.
With the recent rapid increase in resolution, which is represented by high-definition images, high-speed coding apparatuses are desired. In the hybrid coding represented by H.264, an increase in the processing speed of, particularly, an entropy coding apparatus is one factor that dictates the processing speed of the entire coding apparatus.
However, a circuit for performing arithmetic coding that is implemented using the techniques disclosed in the above-described Japanese Patent Laid-Open Nos. 11-103257 and 2005-130099 realizes arithmetic coding of only one symbol during one cycle at the maximum. Thus, it is difficult to realize high-speed arithmetic coding processing.