Motion Compensation on DCT Domain
- PDF / 880,793 Bytes
- 16 Pages / 600 x 792 pts Page_size
- 102 Downloads / 191 Views
otion Compensation on DCT Domain Ut-Va Koc Lucent Technologies Bell Labs, 600 Mountain Avenue, Murray Hill, NJ 07974, USA Email: [email protected]
K. J. Ray Liu Department of Electrical and Computer Engineering and Institute for Systems Research, University of Maryland, College Park, MD 20742, USA Email: [email protected] Received 21 May 2001 and in revised form 21 September 2001 Alternative fully DCT-based video codec architectures have been proposed in the past to address the shortcomings of the conventional hybrid motion compensated DCT video codec structures traditionally chosen as the basis of implementation of standardcompliant codecs. However, no prior effort has been made to ensure interoperability of these two drastically different architectures so that fully DCT-based video codecs are fully compatible with the existing video coding standards. In this paper, we establish the criteria for matching conventional codecs with fully DCT-based codecs. We find that the key to this interoperability lies in the heart of the implementation of motion compensation modules performed in the spatial and transform domains at both the encoder and the decoder. Specifically, if the spatial-domain motion compensation is compatible with the transform-domain motion compensation, then the states in both the coder and the decoder will keep track of each other even after a long series of P-frames. Otherwise, the states will diverge in proportion to the number of P-frames between two I-frames. This sets an important criterion for the development of any DCT-based motion compensation schemes. We also discuss and develop some DCT-based motion compensation schemes as important building blocks of fully DCT-based codecs. For the case of subpixel motion compensation, DCT-based approaches allow more accurate interpolation without any increase in computation. Furthermore, a scare number of DCT coefficients after quantization significantly decreases the number of calculations required for motion compensation. Coupled with the DCT-based motion estimation algorithms, it is possible to realize fully DCT-based codecs to overcome the disadvantages of conventional hybrid codecs. Keywords and phrases: video codec, video coding, MPEG compatibility, motion compensation, DCT.
1. INTRODUCTION In most international video coding standards such as CCITT H.261 [1], MPEG-1 [2], MPEG-2 [3] as well as the proposed HDTV standard, Discrete Cosine Transform (DCT) and block-based motion estimation are the essential elements to achieve spatial and temporal compression, respectively. Most implementations of a standard-compliant codec adopt the conventional motion-compensated DCT video coder and decoder structures as shown in Figures 1a and 1b, respectively. The feedback loop in the coder for temporal prediction consists of a DCT, an Inverse DCT (IDCT), a spatial-domain motion compensator (SD-MC), and a spatial-domain motion estimator (SD-ME) which is usually the full search block matching approach (BKM). This is undesirable. In addition to the additional complexity add
Data Loading...
