A hybrid algorithm is proposed for true motion field estimation. This algorithm consists of three steps: block-based initial motion estimation, image segmentation, and wrong-motion-vector detection and correction based on objects. The hierarchical block-matching algorithms are improved for the initial motion estimation. The improved algorithm uses an adaptive technique to propagate motion vectors between hierarchical levels. It produces accurate motion field everywhere, except in the areas of motion occlusion. In order to correct wrong motion vectors in the areas of motion occlusion, the current image is segmented into objects and an object-based method is proposed to process the estimated motion fields. With the object-based method, wrong-motion vectors are detected by approximating the estimated motion field in each object with a motion model, and are corrected using an object-adaptive interpolator. Experimental results show that the improved hierarchical block-matching algorithm outperforms the conventional hierarchical block-matching algorithms. The proposed algorithm results in dense motion fields that are smooth within every object, discontinuous between objects of different motion, and very close to the true motion fields, (C) 2000 society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)02011-0].

A hybrid algorithm for estimating true motion fields is proposed in this paper. This algorithm consists of three steps: block-based initial motion estimation, image segmentation, and wrong motion vector correction based on objects. The hierarchical block-matching algorithms are improved for the initial motion estimation. The improved algorithm uses an adaptive technique to propagate motion vectors between hierarchical levels. It produces accurate motion field everywhere, except in the areas of motion occlusion. In order to correct wrong motion vectors in the areas of motion occlusion, the current image is segmented into objects and an object-based method is proposed to process the estimated motion fields. With the object-based method, wrong motion vectors are detected by approximating the estimated motion field in each object with a motion model, and are corrected using an object-adaptive interpolator. The object-adaptive interpolator is also used to increase the density of the motion field. Experimental results show that the improved hierarchical block-matching algorithm outperforms the conventional hierarchical block-matching algorithms. The proposed algorithm results in dense motion fields that are smooth within every object, discontinuous between objects of different motion, and very close to the true motion fields.

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This paper descries a technique for representing motion information in a video coder. We present a novel way of representing motion, based on a dictionary of motion models, as well as related estimation techniques. Motion fields are represented by low-order polynomial-based models and a discrete label field. We develop an adaptive context-based entropy coding technique for the label field. In the paper, we address issues relating to rate-distortion optimal coding. Simulations based on a software implementation of the technique are compared to similar results for classical block- based motion compensation and coding techniques.

This paper presents a novel method for representing motion information based on a dictionary of motion models and a tag image which indicates which motion model is used at any given image position. Each model is composed of low-order polynomial-based motion fields. The motion in most sequences can be adequately represented by a very small number of such motion models. We further present an efficient way of estimating and coding this representation. Comparative results are presented which indicate a performance superior to that of motion representations found in classical block-based codecs

We propose a new method for the encoding of label images (also known as segmentation maps or alpha planes) that are often used to identify object location in region-based image and video coders. The method is contour-based and lossless with a contour model composed of two parts: a contour graph describing the topology of the contour network and a directional chain code to deal with the geometric part of the label image (internal contour points). The graph-based description of the topology is designed to minimize the cost of encoding the nodes, while the directional chain codes are compressed by arithmetic coding. The approach is flexible since separating the contour network into topological and geometrical parts allows the use of other lossless or lossy methods to encode the geometric part without changing the graph representation. The proposed method has been compared with an arithmetic encoder used in MPEG-4.

This paper presents a new method for coding the chromatic component of a color image that exploits the piecewise- constant nature of chromatic information. The image is first transformed to a color space in which chromatic information is nearly piecewise constant. The chromatic component is then represented by entries from a codebook of 2D chromatic vectors adapted to the given image. Both memoryless quantization and quantization with spatial memory are considered. Finally, the field of labels is coded using a suitable lossless code with memory; we have used a context- dependent arithmetic code. Experimental results showing rate-distortion performance of the method under various conditions are presented.

We examine the subjective and the objective performance of MPEG-2 main profile/high level for HDTV. Formal subjective assessment was performed by non-expert viewers on the sequences coded at a bit rate of 18 Mbits/s. Since MPEG-2 allows a great flexibility at the encoding end, we also examined the impact of various MPEG-2 encoding parameters on the quality of the reconstructed HDTV video sequences in terms of signal-to-noise ratio (SNR)

This article presents a new approach for planning the dispatching, conflict-free routing, and scheduling of automated guided vehicles in a flexible manufacturing system. The problem is solved optimally in an integrated manner, contrary to the traditional approach in which the problem is decomposed in three steps that are solved sequentially. The algorithm is based on dynamic programming and is solved on a rolling time horizon. Three dominance criteria are used to limit the size of the state space. The method finds the transportation plan minimizing the makespan (the completion time for all the tasks). Various results are discussed. A heuristic version of the algorithm is also proposed for an extension of the method to many vehicles.

We examined the sensitivity of the human visual system to video coding artifacts following a scene cut. Based on classical studies of visual masking, we would expect that sensitivity to coding artifacts would be reduced immediately following a cut. This study focused on the visibility of coding artifacts introduced by an MPEG-2 codec. Three image sequences were selected, each with a scene cut in the middle, such that image content in the first half was different from that in the second half. Using psychophysical methods, visibility threshold were estimated for coding artifacts inserted in the first, second, or third frame following the scene cut. Visibility thresholds were also estimated for coding artifacts that were inserted simultaneously in the first and second frames following the cut. it was found that visual masking effects were present in the first frame following a scene cut, but were virtually absent by the second or the third frame. The results of this research may be used to optimize the behavior of video coding algorithms at scene cuts.

Spatial scalability allows the transmission of images at different levels of resolution in a single bit stream, offering potential spectrum savings with respect to simulcast transmission. The authors consider a two-layer MPEG-2 system which uses spatial scalability to transmit a conventional television signal as a base layer, and an HDTV signal as an enhancement layer or alternatively a conventional television signal as the enhancement and a SIF interlaced signal as the base layer. The issue of interlaced to interlaced conversion, and its effect on the overall performance are studied. The usefulness of the base layer signal in the prediction of the upper layer signal is discussed. Finally, the performance of spatial scalability is compared with a simulcast approach for different bit rates at the lower layer, while keeping the overall bit rate constant

In this paper, we examine the subjective and the objective performance of MPEG-2 for HDTV. Tests were conducted on seven HDTV sequences selected to cover a wide range of conditions in terms of scene content, complexity and motion speed and direction. The selected material was digitized in 4:2:2 format with HDTV resolution and coded using MPEG-2 Man Profile/High Level syntax. Formal subjective assessment was performed by non-expert viewers on the sequences coded at a bit rate of 18 Mbits/s. Since MPEG-2 allows a great flexibility at the encoding end, we also examined the impact of various MPEG-2 encoding parameters on the quality of the reconstructed HDTV video sequences. The parameters include bit rate, the structure of picture organization, as well as temporal processing.

A simple rate control scheme for hybrid DPCM/DCT video coding was presented in [1]. In the rate control scheme, the bit rate regulation is achieved by appropriately selecting the quantization scaling factor for each frame. The quantization scaling factor selection involves an iterative quantization, rate comparison and scaling factor update process. One problem associated with the iterative scheme is that during scene changes, it could take many iterations to reach the final quantization scaling factor because of a lack of a good starting value. This paper presents an adaptive modeling technique incorporated with the iterative rate control scheme to eliminate the long iterative process during scene changes. Both linear and non-linear models are considered. The linear model function models the tangent of the bit rate-scaling factor curve while the non-linear model function models the bit rate-scaling factor curve itself. The models are first determined from the data obtained in the first two iterations and then used to find a scaling factor for the next iteration. This makes it possible to skip a number of unnecessary iterations. The scaling factors used and the bit rates generated are in turn used to refine or update the models. The simulation results indicate that the number of iterations during scene changes is reduced by up to 88%.