Real-Time Imaging最新文献

In this article, we present a new method for visual face tracking that is carried out in a wavelet subspace. Initially, a wavelet representation for the face template is created, which spans a low-dimensional subspace of the image space. The video sequence frames, where the face is tracked, are then orthogonally projected into this subspace. This can be done efficiently through a small number of applications of the wavelet filters. All further computations are performed in the low-dimensional wavelet subspace, allowing real-time processing. An effective performance assessment is carried out to show robustness with respect to facial expression and affine deformations, as well as the efficiency of our method, which allows real-time face tracking.

In this paper, we present a low-complexity ‘reversible variable length code’ (RVLC) decoding scheme for MPEG-4 video that recovers more blocks and sometimes more macroblocks (MBs) from error propagation region of corrupted video packets, as compared to the MPEG-4 scheme. The remaining blocks and MBs are concealed. Simulation studies have been carried out to show that the proposed scheme achieves better data recovery, both in terms of peak-signal-to-noise ratio (PSNR) and perceptual quality. In addition, we present more conditions for error detection than those suggested in MPEG-4, discuss properties of error propagation in corrupted video packets, and provide the RVLC codeword structure. The use of RVLC code structure will enable the decoding in both directions by using only one code table, instead of separate tables used for forward and backward decoding. Since the scheme is purely decoder based, the compliance with the standard is fully maintained. It is very simple for the decoder to keep track of the additional blocks/MBs recovered by the proposed scheme. Therefore, the data recovery scheme suggested in MPEG-4 can still be used as default scheme.

For the low bit-rate multimedia communications, video contents have to be transcoded according to the requirements of network bandwidth and the performance of clients. However, transcoding to the low bit-rate creates video quality degradation (drift error) caused by quantization, motion vector truncation, and downsizing. In this paper, we present an effective motion vector re-estimation method to compensate drift errors in the spatial resolution reduction transcoding. Experimental results show that our method can preserve image quality while transcoding to the low bit-rate.

This paper proposes a performance metrics and a real-time scheduling algorithm based on imprecise computation workload model for delivery of scalable streaming media, which can be adapted to network status and QoS requirement over the best-effort Internet. The scheduling task of a scalable streaming media is partitioned into two subtasks: the mandatory subtask for the base layer and the optional subtask for the enhancement layers. The imprecise computation workload model and real-time scheduling algorithm provide scheduling flexibility by trading off video quality reconstructed in client to meet the playback deadline. Thus, the better usage of available bandwidth and smoother playback are achieved.

Video transcoding is one of the key techniques to provide heterogeneous multimedia applications with Universal Multimedia Access (UMA) service. Recently, compressed domain (DCT, Discrete Cosine Transform) transcoding architectures have been proposed to achieve fast transcoding, in which DCT domain Inverse Motion Compensation (IMC) is the most important module to reduce computational complexity. The problem of IMC has been studied for integer-pixel precision motion vectors (MVs), and, subsequently, for half-pixel precision MVs in which extra filtering, hence, extra computation is introduced. Since most current video coding standards, such as H.263, MPEG-2, etc., use half-pixel precision MVs to achieve better quality, reducing computational complexity of IMC for half-pixel MVs is important for real time fast transcoding video streams encoded by these standards. In this paper, we propose a novel half-pixel filter for IMC, which simplifies the extract operations by integrating the interpolation and translation operations into one single step. Compared to other existing half-pixel filtering algorithms, the proposed filter does not introduce any distortion and drift errors. Experimental results demonstrate that the proposed filter achieves faster transcoding than other DCT domain transcoders, and almost the same video quality as that of pixel domain transcoders.

This paper presents a real-time implementation of Motion-JPEG2000 encoder using a fixed-point DSP chip. Among several modules in JPEG2000 encoder, the lifting algorithm for discrete wavelet transform (DWT) and the embedded block coding with optimized truncation (EBCOT) comprise more than 85% of the encoding complexity. Thus, it is very important to design and optimize these two modules in order to increase the performance of the hardware implementation. First we propose an overlapped block transferring (OBT) method that can significantly improve the performance of the lifting algorithm for DWT by increasing the cache hit rate. We show that the execution time of the lifting scheme can be further reduced by programming the DSP software using the single instruction multiple data (SIMD) instructions and the super scalar pipeline structure. Moreover, we introduce a parallel-pass method for fast implementation of EBCOT. This method reduces the processing time of EBCOT by processing the three coding passes of the same bit-plane in parallel. Experimental results show that our developed Motion-JPEG2000 DSP system meets the common requirement of the real-time video coding [30 frames/s (fps)] and is proven to be a practical and efficient DSP solution.

Wavelet-based coders are widely used in image compression. Many popular embedded wavelet coders are based on a data structure known as zerotree. However, there exists another category of embedded wavelet coders that are fast and efficient without employing zerotree. These coders are based on three key concepts: (1) wavelet coefficient reordering, (2) bit-plane partitioning, and (3) encoding of bit-planes with certain efficient variants of run-length coding. In this paper, we propose a novel method to construct a bit-plane encoder that can be used in this category of non-zerotree coders. Instead of encoding the bit-planes progressively, the bit-plane encoding process can be finished in one pass when multiple bit-plane encoders are activated concurrently. With this proposed method, traditional partitioned-block based parallel processing strategy is enhanced with another dimension (depth of bit-planes) of processing flexibility. This bit-plane encoder inherently targets parallel processing architecture. The final output bitstream can be compatible with that of the original sequential coder if compatibility is preferred over speed and memory efficiency.

A wavelet-based video codec that performs layering of encoded bit streams to support layered scalable video streaming is presented in this paper. The proposed codec can generate separate bit streams comprising different cumulative layers. A new sorting algorithm is incorporated to produce spatial and temporal resolution scalable bit streams, and a specially designed layer-ID is used to identify the layer that a particular data packet belongs to. The proposed codec is more suitable for real network environments as it is able to correctly decode bit streams that have experienced losses incurred during network transmission loss.