This article describes error resilience aspects of the video coding ABSTRACT techniques that are standardized in the IS0 MPEG-4 standard. The article begins with a description of the general problems i n robust wireless video transmission. The specific tools adopted into the 150 MPEG-4 standard t o enable the communication of compressed video data over noisy wireless channels are presented in detail. These techniques include resynchronization strategies, data partitioning, reversible VLCs, and header extension codes. An overview of the evolvina IS0 MPEG-4 standard and its < current status are described.
The problem of establishing reliable and accurate correspondence between a stored 3-D model and a 2-D image of it is important in many computer vision tasks, including model-based object recognition, autonomous navigation, pose estimation, airborne surveillance, and reconnaissance. This paper presents an approach to solving this problem in the context of autonomous navigation of a mobile robot in an outdoor urban, man-made environment. The robot's environment is assumed consist of polyhedral buildings. The 3-D descriptions of the lines constituting the buildings' rooftops is assumed to be given as the world model. The robot's position and pose are estimated by establishing correspondence between the straight line features extracted from the images acquired by the robot and the model features. The correspondence problem is formulated as a twostage constrained search problem. Geometric visibility constraints are used to reduce the search space of possible model-image feature correspondences. Techniques for effectively deriving and capturing these Visibility constraints from the given world model are presented. The position estimation technique presented is shown to be robust and accurate even in the presence of errors in the feature detection, incomplete model description, and occlusions. Experimental results of testing this approach using a model of an airport scene are presented.
This paper presents a solution to the position estimation problem of an autonomous land vehicle navigating in an unstructured mountainous terrain. A digital elevation map (DEM) of the area in which the robot is to navigate is assumed to be given. It is also assumed that the robot is equipped with a camera that can be panned and tilted, a compass, and an altimeter. No recognizable landmarks are assumed to be present in the environment in which the robot is to navigate, and the robot is not assumed to have an initial estimate of its position. The solution presented here makes use of the DEM information, and structures the problem as a constrained search paradigm by searching the DEM for the possible robot location. The shape and position of the horizon line in the image plane and the known camera geometry of the perspective projection are used as parameters to search the DEM. Geometric constraints are used to prune the search space significantly. The algorithm is made robust to errors in the imaging process by accounting for worst case errors. The approach is tested using real terrain data of areas in Colorado and Texas. The method is suitable for use in outdoor mobile robots and planetary rovers.
This paper describes an object-based video coding scheme that was proposed as part of the Texas Instruments' proposal to the emerging ISO MPEG-4 video compression standard. This technique achieves e cient compression by separating coherently moving objects from stationary background and compactly representing their shape, motion and the content. In addition to providing improved coding e ciency at very low bit rates the technique provides the ability to selectively encode, decode and manipulate individual objects in a video stream. This technique supports all the three MPEG4 functionalities that were tested in Nov '95 tests namely, improved coding e ciency, error resilience and content scalability. This paper also describes the error protection and concealment schemes that enable robust transmission of compressed video over noisy communication channels such as analog phone lines and wireless links. The noise introduced by the communication channel is characterized by both burst errors and random bit errors. Applications of this objectbased video coding technology include videoconferencing, video telephony, desktop multimedia and surveillance video.
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