Dr. Yohann Pitrey Profile

Dr. Yohann Pitrey

at Univ Wien

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Publications (3)

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PROCEEDINGS ARTICLE | February 21, 2012

Influence of the source content and encoding configuration on the perceived quality for scalable video coding

Proc. SPIE. 8291, Human Vision and Electronic Imaging XVII

KEYWORDS: Visualization, Databases, Video, Computer programming, Quantization, Light sources and illumination, Video processing, Molybdenum, Video coding, Scalable video coding

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In video coding, it is commonly accepted that the encoding parameters such as the quantization step-size have an influence on the perceived quality. It is also sometimes accepted that using given encoding parameters, the perceived quality does not change significantly according to the encoded source content. In this paper, we present the outcomes of two video subjective quality assessment experiments in the context of Scalable Video Coding. We encoded a large set of video sequences under a group of constant quality scenarios based on two spatially scalable layers. One first experiment explores of the relation between a wide range of quantization parameters for each layer and the perceived quality, while the second experiment uses a subset of the encoding scenarios on a large number of video sequences. The two experiments are aligned on a common scale using a set of shared processed video sequences, resulting in a database containing the subjective scores for 60 different sources combined with 20 SVC scenarios. We propose a detailed analysis of the experimental results of the two experiments, bringing a clear insight of the relation between the encoding parameters combination of the scalable layers and the perceived quality, as well as spreading light on the differences in terms of quality depending on the encoded source content. As an endeavour to analyse these differences, we propose a classification of the sources with regards to their relative behaviour when compared to the average of other source contents. We use this classification to identify potential factors to explain the differences between source contents.

PROCEEDINGS ARTICLE | September 8, 2010

Evaluation of MPEG4-SVC for QoE protection in the context of transmission errors

Proc. SPIE. 7798, Applications of Digital Image Processing XXXIII

KEYWORDS: Switches, Visualization, Video, Error analysis, Computer programming, Temporal resolution, Image enhancement, Molybdenum, Video coding, Scalable video coding

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Scalable Video Coding (SVC) provides a way to encapsulate several video layers with increasing quality and resolution in a single bitstream. Thus it is particularly adapted to address heterogeneous networks and a wide variety of decoding devices. In this paper, we evaluate the interest of SVC in a different context, which is error concealment after transmission on networks subject to packet loss. The encoded scalable video streams contain two layers with different spatial and temporal resolutions designed for mobile video communications with medium size and average to low bitrates. The main idea is to use the base layer to conceal errors in the higher layers if they are corrupted or lost. The base layer is first upscaled either spatially or temporally to reach the same resolution as the layer to conceal. Two error-concealment techniques using the base layer are then proposed for the MPEG-4 SVC standard, involving frame-level concealment and pixel-level concealment. These techniques are compared to the upscaled base layer as well as to a classical single-layer MPEG- 4 AVC/H.264 error-concealment technique. The comparison is carried out through a subjective experiment, in order to evaluate the Quality-of-Experience of the proposed techniques. We study several scenarios involving various bitrates and resolutions for the base layer of the SVC streams. The results show that SVC-based error concealment can provide significantly higher visual quality than single-layer-based techniques. Moreover, we demonstrate that the resolution and bitrate of the base layer have a strong impact on the perceived quality of the concealment.

PROCEEDINGS ARTICLE | January 19, 2009

rho-domain based rate control scheme for spatial, temporal, and quality scalable video coding

Proc. SPIE. 7257, Visual Communications and Image Processing 2009

KEYWORDS: Signal to noise ratio, Modeling, Video, Networks, Control systems, Computer programming, Quantization, Chlorine, Video coding, Scalable video coding

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Rate control is a capital issue in video coding. It allows a regulation of the bitrate out from the encoder, to cope with some network transmission or quality constraints. Scalable Video Coding emerged several years ago as an answer to the growing need of application-adaptable video streams. Although the interest of scalable video coding has been confirrmed by recent studies, it can not be used in practical contexts without proper rate control techniques. In this paper we present a new rate control scheme for scalable video, based on a simple yet attractive bitrate modelling framework called ρ-domain. Our scheme performs accurate rate control on spatial, temporal and quality scalabilities, while maintaining a constant PSNR. Inter layer prediction is also handled effectively.

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