MPEG is traditionally committed to the coding and compression of audio-visual data from natural sources. However, the emerging MPEG-4 standard aims not only at encoding the multiple natural audio-visual objects compos...
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MPEG is traditionally committed to the coding and compression of audio-visual data from natural sources. However, the emerging MPEG-4 standard aims not only at encoding the multiple natural audio-visual objects composing the scene, but also synthetic audio and video to be integrated with the natural objects. It also allows more interaction with both synthetic and natural objects. Networked collaborative virtual environments (NCVEs) have a wide range of different networking requirements. This paper analyzes how these requirements could potentially be met by MPEG-4 and shows that MPEG-4 tools could be extremely useful for the development of such environments.
作者：
Tomas M?ller[a]Ben Trumbore[b][a]Prosolvia Clarus AB
Chalmers University of Technology Gardaviigen S-41250 Gothenberg Sweden E-mail: [b]Program of Computer Graphics Cornell University Ithaca NY 14853 E-mail:
We present a clean algorithm for determining whether a ray intersects a triangle. The algorithm translates the origin of the ray and then changes the base to yield a vector (t u v)T, wheretis the distance to the plane...
We present a clean algorithm for determining whether a ray intersects a triangle. The algorithm translates the origin of the ray and then changes the base to yield a vector (t u v)T, wheretis the distance to the plane in which the triangle lies and (u,v) represents the coordinates inside the *** advantage of this method is that the plane equation need not be computed on the fly nor be stored, which can amount to significant memory savings for triangle meshes. As we found our method to be comparable in speed to previous methods, we believe it is the fastest ray-triangle intersection routine for triangles that do not have precomputed plane equations.
The implementation of an efficient automatic test generation scheme for black box testing is discussed. It uses checkpoint encoding and antirandom testing schemes. Checkpoint encoding converts test generation to a bin...
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The implementation of an efficient automatic test generation scheme for black box testing is discussed. It uses checkpoint encoding and antirandom testing schemes. Checkpoint encoding converts test generation to a binary problem. The checkpoints are selected as the boundary and illegal cases in addition to valid cases to probe the input space. Antirandom testing selects each test case such that it is as different as possible from all the previous tests. The implementation is illustrated using benchmark examples that have been used in the literature. Use of random testing both with checkpoint encoding and without is also reported. Comparison and evaluation of the effectiveness of these methods is also presented. Implications of the observations for larger software systems are noted. Overall, antirandom testing gives higher code coverage than encoding random testing, which gives higher code coverage than pure random testing.
The draft international standard ITU-T H.263 is closely related to the well known and widely used ITU-T Recommendation H.261. However, H.263 does provide the same subjective image quality at less than half the bit-rat...
The draft international standard ITU-T H.263 is closely related to the well known and widely used ITU-T Recommendation H.261. However, H.263 does provide the same subjective image quality at less than half the bit-rate. In this paper we investigate to what extend single enhancements of H.263 contribute to this performance gain, and consider the trade-off quality vs. complexity. Based on typical test sequences, H.263 with its various modes is compared to H.261 on the basis of rate distortion curves at bit-rates up to 128 kbps. At 64 kbps, the performance gain of H.263 in its default mode compared to H.261 is approximately 2 dB. This improvement is achieved with only little increase of complexity, and is mainly due to more accurate motion compensation with half-pel accuracy. Considering the trade-off quality vs. complexity, the combination of the optional coding-modes "Advanced prediction mode" and "PB-frames mode" is a good compromise, resulting in an additional performance gain of 1.5 dB PSNR at 64 kbps. The "Syntax-based arithmetic coding mode" on the other hand, offers only a very small performance gain (0.1 dB at 64 kbps) for its increased computational complexity. Results from profiling an H.263 software codec are presented in order to support complexity considerations of the optional coding-modes.
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