Narciso N. García

Rate control and bit allocation for MPEG-4

In previous years, an interest has developed in the coded representations of video signals allowing independent manipulation of semantically independent elements (objects). Along these lines, the ISO standard MPEG-4 enhances the traditional concept of the video sequence to convert it into a synchronized set of visual objects organized in a flexible way. The real-time generation of a bitstream according to this new paradigm, and suitable for its transmission through either fixed- or variable-rate channels, results in a challenging new bit allocation and rate control problem, which has to satisfy complex application requirements. This paper formalizes this new issue by focusing on the design of rate control systems for real-time applications. The proposed approach relies on the modelization of the source and the optimization of a cost criterion based on signal quality parameters. Different cost criteria are provided, corresponding to a set of relevant definitions of the object priority concept. Algorithms are introduced to minimize the average distortion of the objects, to guarantee desired qualities to the most relevant ones, and to keep constant ratios among the object qualities. The techniques have been applied to a coder implementing the MPEG-4 video verification model, showing good properties in terms of achievement of the control objectives.

NAMA3DS1-COSPAD1: Subjective video quality assessment database on coding conditions introducing freely available high quality 3D stereoscopic sequences

Research in stereoscopic 3D coding, transmission and subjective assessment methodology depends largely on the availability of source content that can be used in cross-lab evaluations. While several studies have already been presented using proprietary content, comparisons between the studies are difficult since discrepant contents are used. Therefore in this paper, a freely available dataset of high quality Full-HD stereoscopic sequences shot with a semiprofessional 3D camera is introduced in detail. The content was designed to be suited for usage in a wide variety of applications, including high quality studies. A set of depth maps was calculated from the stereoscopic pair. As an application example, a subjective assessment has been performed using coding and spatial degradations. The Absolute Category Rating with Hidden Reference method was used. The observers were instructed to vote on video quality only. Results of this experiment are also freely available and will be presented in this paper as a first step towards objective video quality measurement for 3DTV.

Face detection based on a new color space YCgCr

A new color space, YCgCr, is described and applied for face detection. Although similar to the YCbCr color space, it differs in the use of the Cg color component instead of the Cb one. Here, the fundamentals of this new color space YCgCr are presented and its capabilities and advantages over YCbCr are analyzed. After describing the face extraction technique and the required decision values, the parameters which determine the decision thresholds are modeled and represented in the Cg-Cr plane. Based on the representation of the experimental results, the decision thresholds are modified. Finally, the segmentations results achieved with this new color space are compared with those obtained in YCbCr.

Automatic car plate detection and recognition through intelligent vision engineering

License plate recognition systems are becoming the key to many traffic related applications such as road traffic monitoring or parking lot access control. In this paper, a software and hardware architecture implemented in the ESPRIT 5184 LOCOMOTIVE project for automatic vehicle plate number identification is presented. The system, developed in order to dynamically recognize symbol clusters on moving objects, integrates different computer vision techniques related to intrusion detection and automatic pattern recognition in slightly controlled environments, keeping real time operation.

Efficient image segmentation for region-based motion estimation and compensation

An intra-frame segmentation strategy to assist region-based motion estimation and compensation is presented. It is based on the multiresolution application of a histogram clustering and a probabilistic relaxation-labeling algorithm, followed by a local gradient-based bottom-up merging procedure. Specially suited for region-based video coding, it strongly differs from other proposals in that it generates arbitrary shaped image regions with pixel accuracy at a low computational cost, while allowing full reconstruction of the segmentation at the decoder without the transmission of any region description information.

An efficient multiple object detection and tracking framework for automatic counting and video surveillance applications

Automatic visual object counting and video surveillance have important applications for home and business environments, such as security and management of access points. However, in order to obtain a satisfactory performance these technologies need professional and expensive hardware, complex installations and setups, and the supervision of qualified workers. In this paper, an efficient visual detection and tracking framework is proposed for the tasks of object counting and surveillance, which meets the requirements of the consumer electronics: off-the-shelf equipment, easy installation and configuration, and unsupervised working conditions. This is accomplished by a novel Bayesian tracking model that can manage multimodal distributions without explicitly computing the association between tracked objects and detections. In addition, it is robust to erroneous, distorted and missing detections. The proposed algorithm is compared with a recent work, also focused on consumer electronics, proving its superior performance.

Efficient Moving Object Detection for Lightweight Applications on Smart Cameras

Recently, the number of electronic devices with smart cameras has grown enormously. These devices require new, fast, and efficient computer vision applications that include moving object detection strategies. In this paper, a novel and high-quality strategy for real-time moving object detection by nonparametric modeling is presented. It is suitable for its application to smart cameras operating in real time in a large variety of scenarios. While the background is modeled using an innovative combination of chromaticity and gradients, reducing the influence of shadows and reflected light in the detections, the foreground model combines this information and spatial information. The application of a particle filter allows to update the spatial information and provides a priori knowledge about the areas to analyze in the following images, enabling an important reduction in the computational requirements and improving the segmentation results. The quality of the results and the achieved computational efficiency show the suitability of the proposed strategy to enable new applications and opportunities in last generation of electronic devices.

Effect of packet loss in video quality of experience

Today, packet video solutions are found everywhere, mainly due to the many advantages that they offer. Nevertheless, packet losses due to network issues like errors or jitter, affect decoder performance, thus generating video artifacts. The users quality of experience decreases, depending among other factors, on the information carried by the lost packets. In this work we analyze the effect of packet loss in decoded video as a function of the part of the frame affected by the error and how the error is propagated because of temporal prediction. Then, we create a model which makes use of all the information available at the network level in a typical commercial multimedia deployment (such as Internet Protocol television [IPTV]). Finally, we apply that model to the overall design of content-aware network applications governing quality of service measures, video scrambling strategies, and smart retransmission algorithms.

Progressive lower trees of wavelet coefficients: efficient spatial and SNR scalable coding of 3d models

We perform an in-depth analysis of current state-of-the-art waveletbased 3D model coding techniques and then present a new one that outperforms them in terms of compression efficiency and, more importantly, provides full spatial and SNR scalability: PLTW (Progressive Lower Tree Wavelet) coding. As all SNR scalable bit-streams, ours can be used in heterogeneous networks with a wide range of terminals, both in terms of processing power and bandwidth. But because of being spatially scalable, the PLTW bit-stream does not impose on the less powerful terminals the need of building detail trees as deep as required by the maximum LOD, because the wavelet coefficients are sent on a per-LOD basis, thus achieving a “local” SNR scalability within a “global” spatial scalability. In particular, we show that our technique provides a substantial advantage over the only similar one in a current ISO standard (MPEG-4), and thus suggest that PLTW be considered for its future versions.

Subjective assessment of the impact of transmission errors in 3DTV compared to HDTV

Recently, broadcasted 3D video content has reached households with the first generation of 3DTV. However, few studies have been done to analyze the Quality of Experience (QoE) perceived by the end-users in this scenario. This paper studies the impact of transmission errors in 3DTV, considering that the video is delivered in side-by-side format over a conventional packet-based network. For this purpose, a novel evaluation methodology based on standard single stimulus methods and with the aim of keeping as close as possible the home environment viewing conditions has been proposed. The effects of packet losses in monoscopic and stereoscopic videos are compared from the results of subjective assessment tests. Other aspects were also measured concerning 3D content as naturalness, sense of presence and visual fatigue. The results show that although the final perceived QoE is acceptable, some errors cause important binocular rivalry, and therefore, substantial visual discomfort.