Сжатие видео - Postprocessing
|D. Bagni, G. de Haan, V. Riva
|MOTION COMPENSATED POST-PROCESSING FOR LOW BIT RATE VIDEOCONFERENCING ON ISDN LINES
This paper presents a post-processing algorithm for low bit rate videoconferencing on ISDN lines. The relatively few images per second that are transmitted during low bit rate multi-media communications are up-converted after decoding inside the terminal receiver to an increased frame rate of 25 Hz or 30 Hz, depending on the display. Applying advanced motion estimation and compensation techniques can achieve a significant improvement in motion portrayal of moving objects.
RAR 75 кбайт
|Byeungwoo Jeon, and Jechang Jeong
|Blocking Artifacts Reduction in Image Compression with Block Boundary Discontinuity Criterion
Abstract—This paper proposes a novel blocking artifacts reduction method based on the notion that the blocking artifacts are caused by heavy accuracy loss of transform coefficients in the quantization process. We define the block boundary discontinuity measure as the sum of the squared differences of pixel values along the block boundary. The proposed method compensates for selected transform coefficients so that the resultant image has a minimum block boundary discontinuity. The proposed method does not require a particular transform domain where the compensation should take place; therefore, an appropriate transform domain can be selected at the user’s discretion. In the experiments, the scheme is applied to DCT-based compressed images to show its performance.
RAR 427 кбайт
|Sung Deuk Kim, Jaeyoun Yi, Hyun Mun Kim, and Jong Beom Ra
|A Deblocking Filter with Two Separate Modes in Block-Based Video Coding
Abstract—This paper presents a method to remove blocking artifacts in low bit-rate block-based video coding. The proposed algorithm has two separate filtering modes, which are selected by pixel behavior around the block boundary. In each mode, proper one-dimensional filtering operations are performed across the block boundary along the horizontal and vertical directions, respectively. In the first mode, corresponding to flat regions, a strong filter is applied inside the block as well as on the block boundary because the flat regions are more sensitive to the human visual system (HVS) and the artifacts propagated from the previous frame due to motion compensation are distributed inside the block. In the second mode, corresponding to other regions, a sophisticated smoothing filter, which is based on the frequency information around block boundaries, is used to reduce blocking artifacts adaptively without introducing undesired blur. Even though the proposed deblocking filter is quite simple, it improves both subjective and objective image quality for various image features.
RAR 273 кбайт
|Riccardo Bernardini and Guido M. Cortelazzo
|A Post-Processing Technique for Noise Removal of Range Data
Abstract—Spurious range data pose a serious visualization problem with active light systems, as they can totally deform the acquired 3-D shapes. This work presents a technique for their detection based on geometrical considerations. The proposed method does not need extra hardware and can be used effectively as post-processing noise removal provision. The method has been extensively tested on real data. Its performance is discussed and demonstrated by examples.
RAR 766 кбайт
|MLP for Adaptive Postprocessing Block-Coded Images
Abstract—A new technique based on the multilayer perceptron (MLP) neural network is proposed for blocking-artifact removal in block-coded images. The new method is based on the concept of learning-by-examples. The compressed image and its original uncompressed version are used to train the neural networks. In the developed scheme, inter-block slopes of the compressed image are used as input, the difference between the original uncompressed and the compressed image is used as desired output for training the networks. Blocking-artifact removal is realized by adding the neural network’s outputs to the compressed image. The new technique has been applied to process JPEG compressed images. Experimental results show significant improvements in both visual quality and peak signal-to-noise ratio. It is also shown the present method is comparable to other state of the art techniques for quality enhancement in block-coded images.
RAR 109 кбайт
|Guobin Shen and Ming L. Liou
|An Efficient Codebook Post-Processing Technique and a Window-Based Fast-Search Algorithm for Image Vector Quantization
Abstract—Vector quantization is an efficient image-coding technique to achieve a very low bit-rate compression. Furthermore, a lower bit rate can be achieved by equipping the vector quantizer with a memory unit or feedback loop so as to utilize the intervector correlation. For example, predictive vector quantization exploits the linear inter-vector correlation in the spatial domain by a linear vector prediction. Despite the better performance of this kind of vector quantizer, they are usually much more complex. In this paper, we proposed a simple but efficient codebook post-processing technique which enables the vector quantizer to possess higher correlation preservation property. As will be shown, the proposed post-processing technique leads to much higher interindex correlation, or equivalently, smaller first-order (or higher order) entropy. Based on the special pattern of the codebook imposed by the post-processing technique, a window-based fast search (WBFS) algorithm is proposed. The WBFS algorithm not only accelerates the vector quantization processing, but also results in better rate-distortion performance.
RAR 406 кбайт
|Yeonsik Jeong, Inkyeom Kim, and Hyunchul Kang
|A Practical Projection-Based Postprocessing of Block-Coded Images with Fast Convergence Rate
Abstract—At present, block-transform coding is probably the most popular approach for image compression. However, for the sake of its implementation, an image is partitioned into spatially adjoining blocks which are processed independently without considering inter-block correlation. So, this approach inescapably causes an annoying defect called a blocking artifact. In this letter, in order to reduce a blocking artifact appearing in block-coded images, a new quantization constraint set based on the theory of projection onto convex set (POCS) is proposed. This set can efficiently complement the drawbacks of the projection onto the other constraint sets, particularly the smoothness constraint set. Experimental results, using the proposed quantization constraint set as a substitute for the conventional quantization constraint set, show that the postprocessed images not only converge at a fast rate but also obtain better performance in both objective and subjective quality. Moreover, we know that the postprocessed images maintain the clearness of the decoded image before postprocessing.
RAR 739 кбайт
|Hoon Paek, Rin-Chul Kim, and Sang-Uk Lee
|A DCT-Based Spatially Adaptive Post-Processing Technique to Reduce the Blocking Artifacts in Transform Coded Images
Abstract—In this letter, we propose a discrete cosine transform (DCT)-based post-processing technique to alleviate the blocking artifacts in transform coded images. In our approach, the highfrequency components, mainly caused by the edge components, are examined through two steps. First, two adjacent homogeneous blocks from block boundary are found, where the homogeneous block is defined as the block in which no adjacent pixels' difference is larger than the difference of the block boundary. Second, the local frequency characteristics in the homogeneous block are examined through DCT. Then, we derive the relation between the DCT coefficients of two homogeneous blocks of different sizes. By considering the information about the original edge and the relation, we can detect the high-frequency components, mainly caused by the blocking artifact. The performance of the proposed technique is evaluated on both still and moving images. The simulation results indicate that the proposed technique reduces the blocking artifacts effectively and preserves the original edges faithfully, and its performance is very robust to the degree of degradation in decoded images.
RAR 193 кбайт
|Hyun Wook Park and Yung Lyul Lee
|A Postprocessing Method for Reducing Quantization Effects in Low Bit-Rate Moving Picture Coding
Abstract—The reconstructed images from highly compressed MPEG data have noticeable image degradations, such as blocking artifacts near the block boundaries, corner outliers at crosspoints of blocks, and ringing noise near image edges because the MPEG quantizes the transformed coefficients of 8 . 8 pixel blocks. A postprocessing algorithm is proposed to reduce quantization effects, such as blocking artifacts, corner outliers, and ringing noise, in MPEG-decompressed images. The proposed postprocessing algorithm reduces the quantization effects adaptively by using both spatial frequency and temporal information extracted from the compressed data. The blocking artifacts are reduced by one-dimensional (1-D) horizontal and vertical low-pass filtering (LPF), and the ringing noise is reduced by two-dimensional (2-D) signal-adaptive filtering (SAF). A comparison study of the peak signal-to-noise ratio (PSNR) and the computation complexity analysis between the proposed algorithm and the MPEG-4 VM (verification model) postprocessing algorithm is performed by computer simulation with several image sequences. According to the comparison study of PSNR and computation complexity analysis, the proposed algorithm shows better performance than the VM postprocessing algorithm, whereas the subjective image qualities of both algorithms are similar.
RAR 539 кбайт
|Hoon Paek, Rin-Chul Kim, and Sang-Uk Lee
|On the POCS-Based Postprocessing Technique to Reduce the Blocking Artifacts in Transform Coded Images
Abstract—In this paper, we propose a novel postprocessing technique, based on the theory of projections onto convex sets (POCS), to reduce the blocking artifacts in transform-coded images. It is assumed, in our approach, that the original image is highly correlated. Thus, the global frequency characteristics in two adjacent blocks are similar to the local ones in each block. We consider the high-frequency components in the global characteristics of a decoded image, which are not found in the local ones, as the results from the blocking artifact. We employ N-point discrete cosine transform (DCT) to obtain the local characteristics, and 2N-point DCT to obtain the global ones, and then derive the relation between N-point and 2N-point DCT coefficients. A careful comparison of N-point with 2N-point DCT coefficients makes it possible to detect the undesired highfrequency components, mainly caused by the blocking artifact. Then, we propose novel convex sets and their projection operators in the DCT domain. The performances of the proposed and conventional techniques are compared on the still images, decoded by JPEG. The results show that, regardless of the content of the input images, the proposed technique yields significantly better performance than the conventional techniques in terms of objective quality, subjective quality, and convergence behavior.
RAR 360 кбайт
|Yuk-Hee Chan, Sung-Wai Hong, and Wan-Chi Siu
|A Practical Postprocessing Technique for Real-Time Block-Based Coding System
Abstract—In this paper, a noniterative postprocessing method is proposed to restore the images encoded with block-based compression standards such as Joint Photographic Experts Group (JPEG). This method classifies small local boundary regions according to their intensity distribution and then selects appropriate linear predictors to estimate the corresponding boundary pixels in the regions. This approach is easy to implement and we found in our simulations that its restoration performance was very respectable compared with the reported postprocessing methods.
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Подготовили Сергей Гришин и Дмитрий Ватолин