Dr. Thomas Wedi Profile

Dr. Thomas Wedi

at Panasonic R&D Ctr Germany GmbH

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Proceedings Article | 29 January 2007 Paper

Advances in hybrid video coding

Thomas Wedi, Steffen Wittmann, Torsten Palfner, Bernhard Schuur, Florian Knicker

Proceedings Volume 6508, 650812 (2007) https://doi.org/10.1117/12.713078

KEYWORDS: Quantization, Video coding, Image compression, Computer programming, Image filtering, Digital filtering, Video, Error analysis, Matrices, Image quality

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Hybrid video coding is known for a long time and is applied in all video coding standards such as MPEG-x or H.26x. This paper shows that there is still enough potential for further coding efficiency improvements. The paper starts with an overview of state-of-the-art hybrid video coding schemes such as H.264/AVC. Thereafter, our advances on main building blocks of H.264/AVC are presented that significantly improve the coding efficiency. For instance, intra prediction is improved by changing scan directions and thus providing better reference pixels for specific prediction directions. Adaptive filtering and high precision motion compensation improves the motion compensated prediction. Furthermore, the combination of transformation, quantization, and entropy coding of the prediction error is improved using an advanced frequency selective coding technique. With the transmission of post-filter hints it is possible to design a Wiener post-filter that significantly enhances the picture quality. Finally, texture synthesis techniques are used to improve the subjective quality for specific textures with homogenous statistical characteristics. This paper presents our above-mentioned techniques in detail. Depending on the input sequence and the bit rate, the objective and/or subjective gains compared to H.264/AVC are quite significant.

Proceedings Article | 4 January 2002 Paper

Adaptive interpolation filter for motion and aliasing compensated prediction

Thomas Wedi

Proceedings Volume 4671, (2002) https://doi.org/10.1117/12.453082

KEYWORDS: Digital filtering, Error analysis, Electronic filtering, Image filtering, Filtering (signal processing), Motion estimation, Image processing, Quantization, Video coding, Image transmission

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Common motion compensated hybrid video coding standards such as H.263, MPEG-1, MPEG-2, MPEG-4 are based on a fractional-pel displacement vector (DV) resolution of 1/2-pel. Recent approaches like MPEG-4 (ACE-profile) and H.26L use higher DV resolutions of 1/4-pel and 1/8-pel. In order to estimate and compensate fractional-pel displacements, the image signal has to be interpolated. Especially for higher DV resolutions an efficient interpolation filter is necessary. Thus, in MPEG-4 (ACE-profile) and H.26L 6 or 8-tap Wiener interpolation filters are applied. These Wiener filters were designed to interpolate the image signal while reducing spacial aliasing components that deteriorate the motion compensated prediction. In we presented an improved interpolation filter that allows to interpolate an aliasing affected image more accurate then the conventional Wiener filter. This filter is a combination of the Wiener filter and a motion compensated interpolation filter. Up to now these filters are based on invariant filter coefficients. The same coefficients are applied for all sequences and for all images of a sequence. In we presented an adaptive interpolation filter that improves the coding efficiency by reducing the impact of displacement estimation errors and by compensating the aliasing components. The interpolation scheme of is based on filter coefficients that are adapted once per frame to the non-stationary statistical features of the sequence. This paper introduces a motion compensated adaptive interpolation filter that combines the frame-adaptive approach of and the motion compensated interpolation approach of. Due to the motion compensated adaptive interpolation filter, the coding efficiency of an H.26L codec is improved up to 0.8 dB.

Proceedings Article | 29 December 2000 Paper

Hybrid video coding based on high-resolution displacement vectors

Thomas Wedi

Proceedings Volume 4310, (2000) https://doi.org/10.1117/12.411796

KEYWORDS: Electronic filtering, Video coding, Filtering (signal processing), Video, Image filtering, Sinc filters, Image transmission, Linear filtering, Distortion, Image processing

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Common motion compensated hybrid video coding standards such as H.263, MPEG-1, MPEG-2, MPEG-4 are based on a fractional-pel displacement vector resolution of 1/2-pel. Recent approaches like MPEG-4 ACE and H.26L (TML5) use a 1/4-pel displacement vector resolution. In order to estimate and compensate fractional-pel displacements, the image signal has to be interpolated. Therefore different interpolation filters are used in the standards. In this paper an enhanced motion compensated hybrid video codec is presented, which is based on high-resolution displacement vectors. For this purpose, displacement vector resolutions of 1/8- and 1/16-pel are used in order to improve the motion compensated prediction and the coding efficiency. The coding results for different resolutions are presented and the dependence on different interpolation filters is analyzed. It turned out that the higher the displacement vector resolution is, the higher the influence of the filter on the coding gain is. A gain up to 3.0 dB PSNR is obtained compared to a hybrid video codec, which is based on 1/2-pel resolution and bilinear interpolation like H.263, MPEG-1,2,4. Compared to 1/4-pel displacement vector resolution and a wiener interpolation filter as it is used in MPEG-4 ACE and H.26L (TML5), a gain up to 1.0 dB PSNR is obtained.

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