In conventional model-based coding schemes, predefined static models are generally used. These models cannot adapt to new situations, and hence, they have to be very specific and cannot be generated from a single gene...
详细信息
In conventional model-based coding schemes, predefined static models are generally used. These models cannot adapt to new situations, and hence, they have to be very specific and cannot be generated from a single generic model even though they are very similar. In this letter, we present a model-generation technique that can gradually build a model and dynamically modify it according to new video frames scanned. The proposed technique is robust to the object's orientation in the view and can be efficiently implemented with a parallel processing technique. As a result, the proposed technique is more attractive to the practical use of model-based coding techniques in real applications.
We propose a novel model-based coding system for video. model-based coding aims at improving compression gain by replacing the non-informative image elements with some perceptually equivalent models. Images enclosing ...
详细信息
We propose a novel model-based coding system for video. model-based coding aims at improving compression gain by replacing the non-informative image elements with some perceptually equivalent models. Images enclosing large textured regions are ideal candidates. Texture movies are obtained by filming a static texture with a moving camera. The integration of the motion information within the generative texture process allows to replace the 'real' texture with a 'visually equivalent' synthetic one, while preserving the correct motion perception. Global motion estimation is used to determine the movement of the camera and to identify the overlapping region between two successive frames. Such an information is then exploited for the generation of the texture movies. The proposed method for synthesizing 2D + 1 texture movies is able to emulate any piece-wise linear trajectory. The compression performance is very encouraging. On this kind of video sequences, the proposed method improves the compression rate of an MPEG4 state-of-the-art video coder of an order of magnitude while providing a sensibly better perceptual quality. Importantly, the current implementation is real-time on Intel PIII processors. (C) 2002 Elsevier Science B.V. All rights reserved.
To store and transmit the large, amount of image data necessary for Image-based Rendering (IBR), efficient coding schemes are required. This paper presents two different approaches which exploit three-dimensional scen...
详细信息
To store and transmit the large, amount of image data necessary for Image-based Rendering (IBR), efficient coding schemes are required. This paper presents two different approaches which exploit three-dimensional scene geometry for multi-view compression. In texture-basedcoding, images are converted to view-dependent texture maps for compression. In model-aided predictive coding, scene geometry is used for disparity compensation and occlusion detection between images. While both coding strategies are able to attain compression ratios exceeding 2000:1, individual coding performance is found to depend on the accuracy of the available geometry model. Experiments with real-world as well as synthetic image sets show that texture-basedcoding is more sensitive to geometry inaccuracies than predictive coding. A rate-distortion theoretical analysis of both schemes supports these findings. For reconstructed approximate geometry models, model-aided predictive coding performs best, while texture-basedcoding yields superior coding results if scene geometry is exactly known.
Two-dimensional mesh-basedmodels provide a good alternative to motion estimation and compensation. The estimation of the best node-point motion vectors is a challenging task. To this effect, Nakaya and Harashima prop...
详细信息
Two-dimensional mesh-basedmodels provide a good alternative to motion estimation and compensation. The estimation of the best node-point motion vectors is a challenging task. To this effect, Nakaya and Harashima proposed a hexagonal matching procedure. Toklu et al improved the hexagonal search algorithm in terms of both motion-estimation accuracy and computational complexity by employing a hierarchy of regular meshes. Recognizing the limitations of regular meshes, Van Beek et al. extended Toklu et al.'s work by utilizing content-based meshes. Here, we provide an alternative hierarchical motion-estimation method with content-based meshes where hierarchical representations are employed for both the images and the irregular meshes in order to provide further improvements in computational complexity as well as motion accuracy. The comparison results are provided with real video sequences.
MPEG-4 supports the definition, encoding, transmission, and animation of 3-D head and body models. These features can be used for a variety of different applications ranging from low bit-rate video coding to character...
详细信息
MPEG-4 supports the definition, encoding, transmission, and animation of 3-D head and body models. These features can be used for a variety of different applications ranging from low bit-rate video coding to character and avatar animation. In this article, an entire system for the analysis of facial expressions from image sequences and their synthesis is presented. New methods for the estimation of MPEG-4 facial animation parameters as well as scene illumination are proposed. Experiments for different applications demonstrate the potential of using facial animation techniques in video analysis and synthesis. A model-based codec is presented that is able to encode head-and-shoulder video sequences at bit-rates of about 1 kbit/s. Besides the low bit-rate, many enhancements and scene modifications can be easily applied, like scene lighting changes or cloning of expressions for character animation. But also for the encoding of arbitrary sequences, 3-D knowledge can help to increase the coding efficiency. With our model-aided codec, bit-rate reductions of up to 45% at the same quality can be achieved in comparison to standard hybrid video codecs. (C) 2004 Wiley Periodicals, Inc.
In this paper, a next generation 3-D video conferencing system is presented that provides immersive tele-presence and natural representation of all participants in a shared virtual meeting space. The system is based o...
详细信息
ISBN:
(纸本)0819450235
In this paper, a next generation 3-D video conferencing system is presented that provides immersive tele-presence and natural representation of all participants in a shared virtual meeting space. The system is based on the principle of a shared virtual table environment which guarantees correct eye contact and gesture reproduction and enhances the quality of human-centered communication. The virtual environment is modeled in MPEG-4 which also allows the seamless integration of explicit 3-D head models for a low-bandwidth connection to mobile users. In this case, facial expression and motion information is transmitted instead of video streams resulting in bit-rates of a few kbit/s per participant. Beside low bit-rates, the model-based approach enables new possibilities for image enhancements like digital make-up, digital dressing, or modification of scene lighting.
model-based coding is a new image sequence compression technique for very low bit rate coding. Most researchers have paid more attention to facial image analysis and synthesis because facial images are very important ...
详细信息
model-based coding is a new image sequence compression technique for very low bit rate coding. Most researchers have paid more attention to facial image analysis and synthesis because facial images are very important in multimedia communication applications, such as video phone, video conferencing, remote learning etc. This coding method represents the image content in a structural way. This is the reason why model-based coding can get a higher compression ratio (1-10 kb/s) than can the conventional coding methods. In order to encode image signals efficiently, it is necessary to create a suitable generic model and adapt it to the actual object accurately. In this paper, we propose a scheme, based on the integral-projection algorithm, which adapts a face model to an actual face automatically. First, the image is preprocessed by means of edge detection. From the edge mapped image, we use the feature of the increasing sudden edge density to indicate the rough vertical positions of eyes and mouth. According to the local threshold value in each feature area, all of the control points about the eyes and mouth are found. Finally, we use these control points to adapt the model to an actual face.
An integral part of the MPEG-4 standard is the definition of face animation parameters (FAPs). This paper presents a method for the determination of FAPs by using three dimensional (3-D) rigid and nonrigid motion of h...
详细信息
An integral part of the MPEG-4 standard is the definition of face animation parameters (FAPs). This paper presents a method for the determination of FAPs by using three dimensional (3-D) rigid and nonrigid motion of human facial features found from two-dimensional (2-D) image sequences. The proposed method assumes that a 3-D model has been fitted to the first frame of the sequence, tracks the motion of characteristic facial features, calculates the 3-D rigid and nonrigid motion of facial features, and through this, estimates the FAPs as defined by the MPEG-4 coding standard. The 2-D tracking process is based on a novel enhanced version of the algorithm proposed by Kanade, Lucas, and Tomasi. The nonrigid motion estimation is achieved using the same tracking mechanism guided by the facial motion model implied by the MPEG-4 FAPs.
Although several algorithms have been proposed for facial model adaptation from image sequences, the insufficient feature set to adapt a full facial model, imperfect matching of feature points, and imprecise head moti...
详细信息
Although several algorithms have been proposed for facial model adaptation from image sequences, the insufficient feature set to adapt a full facial model, imperfect matching of feature points, and imprecise head motion estimation may degrade the accuracy of model adaptation. In this paper, we propose to resolve these difficulties by integrating facial model adaptation, texture mapping, and head pose estimation as cooperative and complementary processes. By using an analysis-by-synthesis approach, salient facial feature points and head profiles are reliably tracked and extracted to form a growing and more complete feature set for model adaptation. A more robust head motion estimation is achieved with the assistance of the textured facial model. The proposed scheme is performed with image sequences acquired with single uncalibrated camera and requires only little manual adjustment in the initialization setup, which proves to be a feasible approach for facial model adaptation. (C) 2002 Elsevier Science B.V. All rights reserved.
We present a system for finding and tracking a face and extract global and local animation parameters from a video sequence. The system uses an initial colour processing step for finding a rough estimate of the positi...
详细信息
We present a system for finding and tracking a face and extract global and local animation parameters from a video sequence. The system uses an initial colour processing step for finding a rough estimate of the position, size, and inplane rotation of the face, followed by a refinement step drived by an active model. The latter step refines the previous estimate, and also extracts local animation parameters. The system is able to track the face and some facial features in near real-time, and can compress the result to a bitstream compliant to MPEG-4 face and body animation.
暂无评论