11_CM0340_MPEG_Video

11_CM0340_MPEG_Video - 446 JJ II J I Back Close...

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Unformatted text preview: 446 JJ II J I Back Close Compression: Video Compression (MPEG and others) We need to compress video (more so than audio/images) in practice since: 1. Uncompressed video (and audio) data are huge. In HDTV, the bit rate easily exceeds 1 Gbps . big problems for storage and network communications. E.g. HDTV: 1920 x 1080 at 30 frames per second, 8 bits per YCbCr (PAL) channel = 1.5 Gbps . 2. Lossy methods have to be employed since the compression ratio of lossless methods (e.g., Huffman, Arithmetic, LZW) is not high enough for image and video compression. 447 JJ II J I Back Close Not the complete picture studied here Much more to MPEG Plenty of other tricks employed. We only concentrate on some basic principles of video compression: Earlier H.261 and MPEG 1 and 2 standards. with a brief introduction of ideas used in new standards such as H.264 (MPEG-4 Advanced Video Coding) . Compression Standards Committees Image, Video and Audio Compression standards have been specified and released by two main groups since 1985: ISO- International Standards Organisation: JPEG, MPEG. ITU- International Telecommunications Union: H.261 264. 448 JJ II J I Back Close Compression Standards Whilst in many cases one of the groups have specified separate standards there is some crossover between the groups. For example: JPEG issued by ISO in 1989 (but adopted by ITU as ITU T.81) MPEG 1 released by ISO in 1991, H.261 released by ITU in 1993 (based on CCITT 1990 draft). CCITT stands for Comite Consultatif International Telephonique et Telegraphique (International Telegraph and Telephone Consultative Committee) whose parent organisation is ITU. H.262 is alternatively better known as MPEG-2 released in 1994. H.263 released in 1996 extended as H.263+, H.263++. MPEG 4 release in 1998. H.264 releases in 2002 to lower the bit rates with comparable quality video and support wide range of bit rates, and is now part of MPEG 4 (Part 10, or AVC Advanced Video Coding). 449 JJ II J I Back Close How to compress video? Basic Idea of Video Compression: Motion Estimation/Compensation Spatial Redundancy Removal Intraframe coding (JPEG) NOT ENOUGH BY ITSELF? Temporal Greater compression by noting the temporal coherence/incoherence over frames. Essentially we note the difference between frames. Spatial and Temporal Redundancy Removal Intraframe and Interframe coding (H.261, MPEG) 450 JJ II J I Back Close Simple Motion Estimation/Compensation Example Things are much more complex in practice of course . Which Format to represent the compressed data? Simply based on Differential Pulse Code Modulation (DPCM). 451 JJ II J I Back Close Simple Motion Example (Cont.) Consider a simple image (block) of a moving circle....
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11_CM0340_MPEG_Video - 446 JJ II J I Back Close...

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