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Scalable variable complexity approximate forward DCT

Content Provider	IEEE Xplore Digital Library
Author	Lengwehasatit, K. Ortega, A.
Copyright Year	1991
Abstract	The discrete cosine transform (DCT) is one of the major components in most of image and video compression systems. The variable complexity algorithm framework has been applied successfully to achieve complexity savings in the computation of the inverse DCT in decoders. These gains can be achieved due to the highly predictable sparseness of the quantized DCT coefficients in natural image/video data. With the increasing demand for instant video messaging and two-way video transmission over mobile communication systems running on general-purpose embedded processors, the encoding complexity needs to be optimized. In this paper, we focus on complexity reduction techniques for the forward DCT, which is one of the more computationally intensive tasks in the encoder. Unlike the inverse DCT, the forward DCT does not operate on sparse input data, but rather generates sparse output data. Thus, complexity reduction must be obtained using different methods from those used for the inverse DCT. In the literature, two major approaches have been applied to speed up the forward DCT computation, namely, frequency selection, in which only a subset of DCT coefficients is computed, and accuracy selection, in which all the DCT coefficients are computed with reduced accuracy. These two approaches can achieve significant computation savings with minor output quality degradation, as long as the coding parameters are such that the quantization error is larger than the error due to the approximate DCT computation. Thus, in order to be useful, these algorithms have to be combined using an efficient mechanism that can select the "right" level of approximation as a function of the characteristics of the input and the target rate, a selection that is often based on heuristic criteria. In this paper, we consider two previously proposed fast, variable complexity, forward DCT algorithms, one based on frequency selection, the other based on accuracy selection. We provide an explicit analysis of the additional distortion that each scheme introduces as a function of the quantization parameter and the variance of the input block. This analysis then allows us to improve the performance of these algorithms by making it possible to select the best approximation level for each block and a target quantization parameter. We also propose a hybrid algorithm that combines both forms of complexity reduction in order to achieve overall better performance over a broader range of operating rates. We show how our techniques lead to scalable implementations where complexity can be reduced if needed, at the cost of small reductions in video quality. Our hybrid algorithm can speed up the DCT and quantization process by close to a factor of 4 as compared to fixed-complexity forward DCT implementations, with only a slight quality degradation in PSNR.
Sponsorship	IEEE Circuits and Systems Society
Starting Page	1236
Ending Page	1248
Page Count	13
File Size	713754
File Format	PDF
ISSN	10518215
Volume Number	14
Issue Number	11
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2004-11-01
Publisher Place	U.S.A.
Access Restriction	One Nation One Subscription (ONOS)
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Discrete cosine transforms Quantization Video compression Frequency Degradation Approximation algorithms Decoding Mobile communication Encoding Analysis of variance
Content Type	Text
Resource Type	Article
Subject	Electrical and Electronic Engineering Media Technology

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1	Ministry of Education (GoI), Department of Higher Education	Sanctioning Authority	https://www.education.gov.in/ict-initiatives
2	Indian Institute of Technology Kharagpur	Host Institute of the Project: The host institute of the project is responsible for providing infrastructure support and hosting the project	https://www.iitkgp.ac.in
3	National Digital Library of India Office, Indian Institute of Technology Kharagpur	The administrative and infrastructural headquarters of the project	Dr. B. Sutradhar bsutra@ndl.gov.in
4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
5	Website/Portal (Helpdesk)	Queries regarding NDLI and its services	support@ndl.gov.in
6	Contents and Copyright Issues	Queries related to content curation and copyright issues	content@ndl.gov.in
7	National Digital Library of India Club (NDLI Club)	Queries related to NDLI Club formation, support, user awareness program, seminar/symposium, collaboration, social media, promotion, and outreach	clubsupport@ndl.gov.in
8	Digital Preservation Centre (DPC)	Assistance with digitizing and archiving copyright-free printed books	dpc@ndl.gov.in
9	IDR Setup or Support	Queries related to establishment and support of Institutional Digital Repository (IDR) and IDR workshops	idr@ndl.gov.in

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