Efficient Hybrid DCT-Domain Algorithm for Video Spatial Downscaling
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Research Article Efficient Hybrid DCT-Domain Algorithm for Video Spatial Downscaling Nuno Roma and Leonel Sousa INESC-ID/IST, TULisbon, Rua Alves Redol 9, 1000-029 Lisboa, Portugal Received 30 August 2006; Revised 16 February 2007; Accepted 6 June 2007 Recommended by Chia-Wen Lin A highly efficient video downscaling algorithm for any arbitrary integer scaling factor performed in a hybrid pixel transform domain is proposed. This algorithm receives the encoded DCT coefficient blocks of the input video sequence and efficiently computes the DCT coefficients of the scaled video stream. The involved steps are properly tailored so that all operations are performed using the encoding standard block structure, independently of the adopted scaling factor. As a result, the proposed algorithm offers a significant optimization of the computational cost without compromising the output video quality, by taking into account the scaling mechanism and by restricting the involved operations in order to avoid useless computations. In order to meet any system needs, an optional and possible combination of the presented algorithm with high-order AC frequency DCT coefficients discarding techniques is also proposed, providing a flexible and often required complexity scalability feature and giving rise to an adaptable tradeoff between the involved scalable computational cost and the resulting video quality and bit rate. Experimental results have shown that the proposed algorithm provides significant advantages over the usual DCT decimation approaches, both in terms of the involved computational cost, the output video quality, and the resulting bit rate. Such advantages are even more significant for scaling factors other than integer powers of 2 and may lead to quite high PSNR gains. Copyright © 2007 N. Roma and L. Sousa. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
In the last few years, there has been a general proliferation of advanced video services and multimedia applications, where video compression standards, such as MPEG-x or H.26x, have been developed to store and broadcast video information in the digital form. However, once video signals are compressed, delivery systems and service providers frequently face the need for further manipulation and processing of such compressed bit streams, in order to adapt their characteristics not only to the available channel bandwidth but also to the characteristics of the terminal devices. Video transcoding has recently emerged as a new research area concerning a set of manipulation and adaptation techniques to convert a precoded video bit stream into another bit stream with a more convenient set of characteristics, targeted to a given application. Many of these techniques allow the implementation of such processing operations directly in the compressed precoded video streams, thus offering significant advantages in what
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