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A method that increases the error resistance of the HDTV system and offers graceful picture degradation in the presence of bit errors, is presented. Due to the nature of the presently proposed compression schemes for HDTV systems, an error in a data bit does not only affect the block the bit belongs to, but unfortunately the effects of this error may perpetuate to the following blocks. This is because a bit error may cause loss of synchronization between the data bits and the picture blocks they represent. Our method restricts the effects of a bit error to a picture block whose size is significantly smaller than those used by the HDTV systems. We achieve synchronization by transmitting a header-word for each such synchronization block. Each header-word contains the number of data bits representing the compressed block. This header-word is protected by two levels of FEC code. To decrease the number of extra bits needed by the header-words, two different synchronization block sizes are used, a relatively small block size for the reference frames and a larger size for the inter-frames. The resulting method improves the quality of the picture in the presence of errors and defers the SNR at which the HDTV picture suddenly deteriorates by 2.5 to 3 dB. It also allows operation at higher order modulation transmission schemes, e.g., 32-QAM instead of 16-QAM, without the requirement of increased signal power 相似文献
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The tradeoff between picture quality and bandwidth usage is a prominent issue in the world of broadcasting. Since broadcasters are able to transmit multiple streams simultaneously in a channel, they face the challenge of guaranteeing the contracted picture quality required by each of the transmitted video streams while maximizing the number of video streams carried in each channel. We have developed an easy to implement MPEG-2 based multi-program video coding system suitable for digital TV broadcast, video on demand, and high definition TV over broadcast satellite networks with limited bandwidth. Compared to present broadcast systems and for the same level of contracted picture quality, our system greatly increases the number of video streams transmitted in each channel. As a result, either a large number of transponders can be freed to carry real-time broadcasting or the level of picture quality can be significantly increased. By switching from tape storage to video server technology, the need for numerous playback (VTR) systems at the headend is eliminated. In addition, the most of the complete MPEG-2 encoders are replaced by much less complex MPEG-2 transcoders. All this means a much more cost-effective solution for broadcast stations. 相似文献
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Sanchez V. Nasiopoulos P. Abugharbieh R. 《IEEE transactions on information technology in biomedicine》2008,12(4):442-446
This paper presents an efficient lossless compression method for 4-D medical images based on the advanced video coding scheme (H.264/AVC). The proposed method efficiently reduces data redundancies in all four dimensions by recursively applying multiframe motion compensation. Performance evaluations on real 4-D medical images of varying modalities including functional magnetic resonance show an improvement in compression efficiency of up to three times that of other state-of-the-art compression methods such as 3D-JPEG2000. 相似文献
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A compression technique which preserves edges in compressed pictures is developed. The proposed compression algorithm adapts itself to the local nature of the image. Smooth regions are represented by their averages and edges are preserved using quad trees. Textured regions are encoded using BTC (block truncation coding) and a modification of BTC using look-up tables. A threshold using a range which is the difference between the maximum and the minimum grey levels in a 4×4 pixel quadrant is used. At the recommended value of the threshold (equal to 18), the quality of the compressed texture regions is very high, the same as that of AMBTC (absolute moment block truncation coding), but the edge preservation quality is far superior to that of AMBTC. Compression levels below 0.5-0.8 b/pixel may be achieved 相似文献
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We present a new compression method which compresses 8×8 picture blocks by fixed-length codewords. The compression operation is performed on the discrete cosine transforms, DCT, of each block. As a result, our method combines the distinct advantage of being fixed-length with the high image quality obtained by the DCT based compression methods. Our method has excellent error-resistance characteristics since it does not have the synchronization and error propagation problems inherent in variable-length coding methods 相似文献
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