共查询到10条相似文献,搜索用时 93 毫秒
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We consider the use of pre and postfilters in conjunction with M-channel, uniform-band paraunitary (orthonormal) filter banks. We show that given any orthonormal filter bank, the pre and postfilters that maximize the coding gain are determined entirely by the power spectrum of the input process regardless of the details of the orthonormal filter blank (which could be FIR, IIR, or even the ideal brickwall filter bank). The optimized coding gain, however, depends on the prefilter as well as the sandwiched orthonormal filter bank. The coding gain improvement due to pre and postfiltering is often significant as we demonstrate with numerical examples and comparisons. The validity of our results depends strongly on the orthonormality property of the filter bank in between the pre and postfilters. In the nonorthonormal case, most of these results are not true, as is demonstrated 相似文献
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《Solid-State Circuits, IEEE Journal of》1986,21(6):956-963
New video transmission systems such as the satellite D2-MAC/packet system and second-generation local area networks for video-communications will use digital coding and decoding of video signals. To develop reliable and low-cost receivers, it appears necessary to implement the main functions using CMOS technology. Therefore many analog functions must be replaced by the equivalent digital ones before implementation. Digital circuits are described for the final video postprocessing, i.e. video postfiltering and dematrixing. An NMOS digital filter for Y, CR, and CB oversampling is presented. R, G, and B components are obtained using a CMOS matrix operator, also described. These two circuits are used in a 108-Mb/s experimental video decoder. 相似文献
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《Journal of Visual Communication and Image Representation》2014,25(7):1507-1515
Coding artifacts are annoying in highly compressed signals. Most of the existing artifact reduction methods are designed for one specific type of artifacts, codecs, and bitrates, which are complex and exclusive for one type of artifact reduction. Since both the compressed image/video and the coding error contain information of the original signal, they are highly correlated. Therefore, we try to recover some lost data based on the correlation between the compressed signal and the coding error, and introduce a novel and universal artifact reduction method. Firstly, according to the spatial correlation among pixels, a pixel-adaptive anisotropic filter is designed to reconstruct the distorted signal. Next, a globally optimal filter is designed to further recover the coding loss. Experimental results demonstrate that within an extensive range of bitrates, the proposed method achieves about 0.8 dB, 0.45 dB, 0.3 dB, and 0.2 dB on average of PSNR improvement for JPEG, MPEG4, H.264/AVC, and HEVC compressed signals, respectively. 相似文献
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Lu Gan Chengjie Tu Jie Liang Trac D Tran Kai-Kuang Ma 《IEEE transactions on image processing》2007,16(2):428-441
It has been well established that critically sampled boundary pre-/postfiltering operators can improve the coding efficiency and mitigate blocking artifacts in traditional discrete cosine transform-based block coders at low bit rates. In these systems, both the prefilter and the postfilter are square matrices. This paper proposes to use undersampled boundary pre- and postfiltering modules, where the pre-/postfilters are rectangular matrices. Specifically, the prefilter is a "fat" matrix, while the postfilter is a "tall" one. In this way, the size of the prefiltered image is smaller than that of the original input image, which leads to improved compression performance and reduced computational complexities at low bit rates. The design and VLSI-friendly implementation of the undersampled pre-/postfilters are derived. Their relations to lapped transforms and filter banks are also presented. Two design examples are also included to demonstrate the validity of the theory. Furthermore, image coding results indicate that the proposed undersampled pre-/postfiltering systems yield excellent and stable performance in low bit-rate image coding. 相似文献
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《Signal Processing, IEEE Transactions on》2001,49(3):593-602
Subband echo cancelers decompose their input signals into frequency bands and then do echo canceling on a per-band basis. Such structures have both computational and algorithmic advantages over conventional full-band structures. However, many implementations have been found to suffer from slow convergence at band edges, that is, at frequencies carried roughly equally by two adjacent subbands. A poorly conditioned correlation matrix with eigenvalues approaching zero is generally cited as the culprit. One possible solution to the poor band-edge convergence problem is a scheme dubbed postfiltering by Morgan (1995) and De Leon (1995). Under postfiltering, the slowly converging eigenmodes continue to be excited, but their energy is removed from the final output. An alternative solution developed here makes the subband analysis filter for the reference signal slightly broader in spectrum than the analysis filter for the echo. With unequal analysis filtering, it is possible to avoid eliciting the bad eigenmodes in the first place. There are important practical advantages for unequal analysis filtering. Extreme care must be exercised in filter design. However, given a proper understanding of requirements, it is possible to synthesize reasonable-length FIR filters with entirely satisfactory performance 相似文献
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HEVC in-loop deblocking filter significantly improves the subjective quality of coded video by removing blocking artifact. However, there are still visible blocking artifacts in the complex videos with fast and chaotic motions coded at a low bitrate. In this paper, we propose a three-step deblocking filter scheme, which pre-processes video to remove undesired noise, next removes the corner outliers, and then suppresses the normal blocking artifacts with adaptive deblocking filters. The whole deblocking filtering process is applied on both luma and chroma components. Experimental results show that the proposed method could effectively improve the subjective quality for various videos, and outperform other typical post-processing deblocking methods. 相似文献
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《Signal Processing, IEEE Transactions on》2008,56(12):5851-5860
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《IEEE transactions on image processing》2009,18(6):1166-1178