Hans L. Cycon

Very low bit-rate video coding using wavelet-based techniques

In this paper, we propose a very low bit-rate video coding scheme based on a discrete wavelet transform (DWT), block-matching motion estimation (BME), and overlapped block motion compensation (OBMC). Our approach reveals that the coding process works more efficiently if the quantized wavelet coefficients are preprocessed by a mechanism exploiting the redundancies in the wavelet subband structure. Thus, we introduce a new framework of preceding techniques based on the concepts of partitioning, aggregation, and conditional coding (PACC). Our experimental results show that our PACC coder outperforms the VM (Version 5.1) of MPEG4 both for the coding of intraframes (1-2 dB PSNR) and residual frames (up to 1.5 dB PSNR) of typical MPEG4 test sequences. The subjective quality of reconstructed video is, in general, superior to that obtained from the VM implementation. In addition, when restricted to the intraframe mode, the proposed coding algorithm produces results which are among the best reported for still image compression.

Performance evaluation of Motion-JPEG2000 in comparison with H.264/AVC operated in pure intracoding mode

Recently, two new international image and video coding standards have been released: the wavelet-based JPEG2000 standard designed basically for compressing still images, and H.264/AVC, the newest generic standard for video coding. As part of the JPEG2000 suite, Motion-JPEG2000 extends JPEG2000 to a range of applications originally associated with a pure video coding standard like H.264/AVC. However, currently little is known about the relative performance of Motion-JPEG2000 and H.264/AVC in terms of coding efficiency on their overlapping domain of target applications requiring the random access of individual pictures. In this paper, we report on a comparative study of the rate-distortion performance of Motion-JPEG2000 and H.264/AVC using a representative set of video material. Our experimental coding results indicate that H.264/AVC performs surprisingly well on individually coded pictures in comparison to the highly sophisticated still image compression technology of JPEG2000. In addition to the rate-distortion analysis, we also provide a brief comparison of the evaluated coding algorithms in terms of complexity and functionality.

Global serverless videoconferencing over IP

In recent years the capabilities of the common Internet infrastructure have increased to an extent where data intensive communication services may mature to become popular, reliable applications. Videoconferencing over IP can be seen as such a highly prominent candidate. However, heavy infrastructure and complicated call handling hinder acceptance of standard solutions.This paper presents a more lightweight framework--both communication scheme and conferencing software--to overcome these deficiencies. A simple, ready-to-use global location scheme for conference users is proposed. First practical experiences are reported.

A FAST WAVELET-BASED VIDEO CODEC AND ITS APPLICATION IN AN IP VERSION 6-READY SERVERLESS VIDEOCONFERENCING SYSTEM

The purpose of this paper is twofold: On the one hand, we propose a fast wavelet-based video codec which is implemented into a real-time video conferencing tool. The proposed codec uses temporal frame difference coding, a computationally low-complex 5/3 tap wavelet transform, and a fast entropy coding scheme based on Golomb–Rice codes. On the other hand, we present an application of the video conferencing tool in a serverless peer-to-peer IP-based communication framework. For mobile communication we propose a simple, ready-to-use location scheme for video conference users in a global network.

Context-based denoising of images using iterative wavelet thresholding

In this paper, we propose a spatially adaptive wavelet thresholding method using a context model that has been inspired by our prior work on image coding. The proposed context model relies on an estimation of the weighted variance in a local window of scale and space. Appropriately chosen weights are used to model the predominant correlations for a reliable statistical estimation. By iterating the context-based thresholding operation, a more accurate reconstruction can be achieved. Experimental results show that our proposed method yields significantly improved visual quality as well as lower mean squared error compared to the best recently published results in the denoising literature.

Image denoising using fractal- and wavelet-based methods

There is a considerable amount of literature about image denoising using wavelet-based methods. Some new ideas where also reported using fractal methods. In this paper we propose a hybrid wavelet-fractal denoising method. Using a non-subsampled overcomplete wavelet transform we present the image as a collection of translation invariant copies in different frequency subbands. Within this multiple representation we do a fractal coding which tries to approximate a noise free image. The inverse wavelet transform of the fractal collage leads to the denoised image. Our results are comparable to some of the most efficient known denoising methods.

Peer-to-peer videoconferencing with H.264 software codec for mobiles

A rapidly growing number of carriers offer wireless video services to their customers, taking advantage of high quality video codecs implemented in dedicated hardware of selected mobile devices. In this paper we introduce a video conferencing software, which seamlessly integrates mobile with stationary users in a provider and device independent fashion. Innovations of this work are twofold. At first we report on a mobile realization of an H.264 video codec and its performance on a standard consumer Smartphone. Operating within the tight bounds of real-time compliance on mobiles, this software is an adapted version of a highly optimized H.264 codec. This DAVC codec, which we introduce along the line, significantly out-performs compatible H.264 realizations and allows for a scalable adaptation of its frame rate. In the second part we present a barrier-resistant peer-to-peer group communication scheme, which scales well for medium-size conferences and accounts for the heterogeneous nature of mobile and stationary participants. An outlook on mobility related group communication issues and future optimizations based on structured communication layers concludes the work.

A temporally scalable video codec and its applications to a video conferencing system with dynamic network adaption for mobiles

In this paper we present a multipoint video conferencing system that adapts to heterogeneous members including mobiles. The system is built upon a low complexity scalable extension of our H.264 codec DAVC, and a congestion-aware dynamic adaptation layer. We show that our temporally scaled video codec DSVC has the same RD performance as the non-scaled version with comparable configuration. We achieve this by QP cascading, i.e., assigning gradually refining quantization parameters to the declining temporal layers. The different quantization of frames does not lead to visually distinguishable quality fluctuations. We also present and analyze a mobile-compliant version of DSVC at reduced complexity that still admits comparable performance. Finally, we report on early work of dynamic layer tuning. Derived of delay variation measures, senders exploit scalable video layering to adapt the video transmission to varying network conditions. Initial results indicate that video performance remains close to optimal.

Design of a highly efficient wavelet-based video coding scheme

In this paper, we present a novel design of a wavelet-based video coding algorithm within a conventional hybrid framework of temporal motion-compensated prediction and transform coding. Our proposed algorithm involves the incorporation of multi-frame motion compensation as an effective means of improving the quality of the temporal prediction. In addition, we follow the rate-distortion optimizing strategy of using a Lagrangian cost function to discriminate between different decisions in the video encoding process. Finally, we demonstrate that context-based adaptive arithmetic coding is a key element for fast adaptation and high coding efficiency. The combination of overlapped block motion compensation and frame-based transform coding enables blocking-artifact free and hence subjectively more pleasing video. In comparison with a highly optimized MPEG-4 Advanced Simple Profile coder, our proposed scheme provides significant performance gains in objective quality of 2.0-3.5 dB PSNR.

Video coding using a bilinear image warping motion model and wavelet-based residual coding

This paper describes a video coding algorithm that combines new ideas in motion estimation, wavelet filter design, and wavelet-based coding techniques. A motion compensation technique using image warping and overlapped block motion compensation is employed to reduce temporal redundancies in a given image sequence. This combined motion model has the advantage of representing more complex motion than simple block matching schemes. Spatial decorrelation of the motion compensated residual images is performed using an one- parametric family of biorthogonal IIR wavelet filters coupled with a highly efficient pre-coding scheme. Experimental results demonstrate substantial improvements in objective quality of 1.0 - 2.2 dB PSNR compared to the H.263+ standard. Especially at very low bit-rates where the reconstruction quality of block-based coders suffers from visually annoying blocking artifacts the proposed coding scheme produces a superior subjective quality.