opticom.de

Perceptually motivated spatial and temporal integration o

Chair of Multimedia Communications

In this paper we present algorithms developed for transcoding predicted intra macroblocks between H.263 and H.264. It can be used in video servers for fast adaption of video content in networks supplying different coding standards, e.g. internet and UMTS. It is shown that due to basic pattern similarities between frequency domain prediction of H.263 and spatial prediction of H.263 it is possible to reuse predictor side information. This side information is used to simplify the mode and direction decision for intra prediction. It results in a high reduction of complexity for mode and direction estimation at comparable PSNR and a slightly increased rate. 1

Overview of LowComplexity Video Transcoding From H.263 to H.264

With the standardization of H.264/AVC by ITU-T and ISO/IEC and the adaptatation into new hardware, the necessity of transcoding between existing standards and H.264 will arise to achieve interoperability between hardware devices. Because of the many new prediction parameters as well as the pixel-based deblocking filter and the new transform of H.264 this is a difficult task to perform. In our work we propose a fast cascaded pixel-domain transcoder from H.263 to H.264 for both intra- and inter-frame coding. The rate-distortion (RD) performance of the encoded bitstreams is compared to an exhaustive full-search approach. Our approach leads to 9 % higher data rate in average, but the computational complexity for the prediction can be reduced by 90 % and more. It will be shown that the algorithms proposed for H.263 are applicable for transcoding MPEG-2 to H.264, too. 1

On Requantization in Intra-Frame Video Transcoding with Different Transform Block Sizes

Abstract — Transcoding is a technique to convert one video bitstream into another. While homogeneous transcoding is done at the same coding standard, inhomogeneous transcoding converts from one standard format to another standard. Inhomogeneous transcoding between MPEG-2, MPEG-4 or H.263 was performed using the same transform. With the standardisation of H.264 also a new transform basis and different block size was defined. For requantization from block size��to��this leads to the effect that the quantization error of one coefficient in a block of size��is distributed over multiple coefficients in blocks of size��. In our work, we analyze the requantization process for inhomogeneous transcoding with different transforms. The deduced equations result in an expression for the correlation of the error contributions from the coefficients of block size ��at each coefficient of block size��. We then compare the mathematical analysis to simulations on real sequences. The reference to the requantization process is the direct quantization of the undistorted signal. It will be shown that the loss is as high as 3 dB PSNR at equivalent step size for input and output bitstream. Also an equation for the choice of the second quantization step size in dependency of the requantization loss is deduced. The model is then extended from the DCT to the integer-based transform as defined in H.264. I

Multimed Tools Appl DOI 10.1007/s11042-007-0126-7 Fast video transcoding from H.263 to H.264/MPEG-4 AVC

Abstract In the past 10 years detailed works on different video transcoders have been published. However, the new ITU-T Recommendation H.264—also adapted as ISO/IEC MPEG-4 Part 10 (AVC)—provides many new encoding options for the prediction processes that lead to difficulties for low complexity transcoding. In this work we present very fast transcoding techniques to convert H.263 bitstreams into H.264/AVC bitstreams. We will give reasoning, why the proposed pixel domain approach is advantageous in this scenario instead of using a DCT domain transcoder. Our approach results in less than 9 % higher data rate at equivalent PSNR quality compared to a full-search approach. But this rate loss allows the reduction of the search complexity by a factor of over 200 for inter frames and still a reduction of over 70 % for intra frames. A comparison to a fast search algorithm is given. We also provide simulation results that our algorithm works for transcoding MPEG-2 to H.264/AVC in the aimed scenario. Keywords Video transcoding · Low complexity coding · H.263 · H.264/MPEG-4 AVC

INFLUENCE OF THE PRESENTATION TIME ON SUBJECTIVE VOTINGS OF CODED STILL IMAGES

The quality of coded images is often assessed by a subjective test. Usually the viewers get as much time as they need to find a stable result. In video sequences however, the viewer has to judge the quality in a shorter time that is defined by the changing content or a following scene cut. Therefore it is desirable to know the influence of a shorter presentation time on the perceptibility of distortions. In this paper we present the results of a suitable subjective test on coded still images. The images were presented for six different durations, ranging from 200 ms to 3 s. Special care was taken to avoid the memorization effect usually present after short presentations. The results show that the viewers tend to avoid extreme votings at short durations. The variance of the votings is also discussed in detail. Based on the result of the voting for the longest presentation time, we propose a prediction model for the voting of the shorter durations using a logistic curve fit. This Presentation Time Model (PTM) is presented and analysed in detail

Simplified Mode-Matching Techniques for the Analysis of Coaxial-Cavity-Coupled Radial E-Plane Power Dividers

Two simplified mode-matching techniques for the numerical analysis of nonsymmetric waveguide E-plane radial N-ports are presented. The first model, which utilizes cartesian and cylindrical coordinate systems for interfacing rectangular waveguides to a coaxial cavity, shows excellent agreement between measurements and computer-intensive finite-element calculations. The second technique, which is based on rectangular coordinates only and thereby neglects the curvature of the coaxial cavity, achieves agreement only for transmission coefficients if the inner radius of the coaxial cavity is sufficiently large. The software for both models are operational on personal computers and require only seconds for a complete analysis. Examples are presented for a Ku-band E-plane six-port and a W-band E-plane ratrace ring. Some additional investigations on the ratrace configuration demonstrate the applicability of the models with respect to reliable component design