The quantized DCT and its application to DCT-based video coding

TitleThe quantized DCT and its application to DCT-based video coding
Publication TypeJournal Article
Year of Publication2002
AuthorsDocef, A., F. Kossentini, K. Nguuyen-Phi, and I. R. Ismaeil
JournalImage Processing, IEEE Transactions on
Pagination177 -187
Date Publishedmar.
Keywords2D discrete cosine transform, add operations, computational complexity, DCT-based video coding, discrete cosine transforms, H.263 video encoding, image sequences, low bit rate coding, MPEG-2 video encoding, multiplierless implementation, multiplierless integer implementation, optimisation, quantisation (signal), quantization, quantized DCT, shift operations, transform coding, video coding, video encoder

The two-dimensional (2-D) discrete cosine transform (DCT) and the subsequent quantization of the transform coefficients are two computationally demanding steps of any DCT-based video encoder. In this paper, we propose an efficient joint implementation of these two steps, where the precision in computing the DCT can be exchanged for a reduction in the computational complexity. First, the quantization is embedded in the DCT, thus eliminating the need to explicitly quantize the transform coefficients. A multiplierless integer implementation of the quantized DCT (QDCT) is then proposed that performs shift and add operations instead of full multiplications. A sequence of multiplierless QDCT algorithms is obtained with increasing precision and number of computations. Finally, further savings in computations are obtained by terminating the DCT computations whenever intermediate results indicate that the transform and quantization steps will likely result in a block of zero values. The proposed algorithms are applied to, and results are presented for, high-quality MPEG-2 and low bit rate H.263 video encoding


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