Copyright 2000 IEEE. Published in the 2000 International Conference on Image Processing (ICIP-2000), scheduled for September 10-13, 2000 in Vancouver, BC. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works, must be obtained from the IEEE. Contact: Manager, Copyrights and Permissions / IEEE Service Center / 445 Hoes Lane / P.O. Box 1331 / Piscataway, NJ 08855-1331, USA. Telephone: + Intl. 908-562-3966.
ADAPTIVE POST-PROCESSING ERROR CONCEALMENT BASED ON FEEDBACK FROM A VIDEO-SURVEILLANCE SYSTEM Fabrizio Granelli, Franco Oberti and Carlo Regazzoni University of Genoa, Department of Biophysical and Electronic Engineering (DIBE) Via all’Opera Pia 11A - 16145 Genova (Italy) e-mail:
[email protected] ABSTRACT An effective real-time post-processing algorithm for error recovery in noise corrupted JPEG bit streams integrated into an existing remote video-surveillance system is presented1. The algorithm exploits information extracted by the video-surveillance system in order to detect corrupted frames and to recover them, enhancing the performances of the system, without compromising the real-time behavior of the application. Results show the validity of the presented approach.
1. INTRODUCTION The joined diffusion of advanced video-sensor and commercial Wireless LAN transmission technologies makes the interest for outdoor Multimedia video-based surveillance (MSS) applications more and more growing [1]. However, some technical problems, arising from the integration of MSSs with existing wireless LANs are still to be faced in an effective way. These problems mainly consist in the strict bandwidth constraints imposed on the upstream transmission of multimedia information from remotely guarded sites to the network head-end. [1]. In order to cope with the upstream bandwidth limitations characterizing the existing wireless networks, there is the necessity of employing source-coding techniques for reducing the source bandwidth of the transmitted information. Transmission of compressed digital video signal is usual in all kinds of multimedia services. Digital wireless cameras for remote AVS applications generally use JPEG [2] (or MJPEG [3]) compression coding, as these methods can provide a better quality of the images than the MPEG [3] one. However, wireless channels are subject to many noisy impairments and fluctuations and JPEG coding is quite vulnerable to the effects of 1
This work has been partially supported by the University and Scientific Research Ministry (MURST) of the Italian Government under the National Interest Scientific Research Program
transmission errors. For this reason an effective error concealment strategy [4] is required especially by those applications, such as remote MS ones, characterized by high reliability constraints. In [5] an error correction algorithm for remote MS applications was presented. This algorithm makes a preprocessing of the corrupted images before being processed by a surveillance system. In this paper, a post-processing error concealment integrated into such a system is presented. The performances of the application considered in [6] (i.e. prevention of vandal acts inside metro-railway stations) are validated and enhanced through the integration of a real-time post-processing algorithm that enables the reconstruction of the JPEG images corrupted by channel noise. Such algorithm exploits information on the background of the scene and on objects movement, which is directly extracted by the video-surveillance system. In this sense, the proposed system, according to our knowledge, is one of the first real-time applications to integrate image interpretation and error concealment strategies in a low cost, PC-based architecture. The paper is organized as follows: Section 2 contains the video-surveillance system description, Section 3 describes the post-processing algorithm that integrates into the video-surveillance system. Section 4 presents the obtained results and finally conclusions are drawn in Section 5. 2. SYSTEM DESCRIPTION The video-surveillance application considered is the remote monitoring of metro stations in order to detect and prevent vandal acts. The AVS-PV project [6] (19971998), funded by European Union aimed at assisting a human operator in the surveillance of unmanned metro stations. A color camera acquires image sequences from a metro station. Such sequences are then digitized and coded using JPEG compression before transmission to a remote processing centre in which the sequences are processed.
Figure 1 shows the block diagram of the MSS system with the proposed integrated error concealment module. X U
Y
Y
W
Z
[
2
4
.
5
]
/
6
^
W
-
1
R
,
3
+
1
\
0
4
7
5
2
8
;
!
"
$
%
&
E
I
J
>
K
R
S
N
O
U
P
V
