Post-Filtering Of Transforms-Coded Images

Tzou, Kou-Hu

doi:10.1117/12.948449

Cited by 21 publications

(17 citation statements)

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“…where , , and are defined in a manner similar to (21) and (22). Thus, the total MSDS (hereafter, MSDS ) considered The form of MSDS used in the proposed methods of [33] and [34] is MSDS which, as mentioned above, involves only the horizontal and vertical adjacent blocks for its computation and thus does not use the intensity slopes of the four diagonally adjacent blocks.…”

Section: Reduction Of Blocking Artifact In the Frequency Domainmentioning

confidence: 99%

“…Reeves and Lim [8] apply the 3 3 Gaussian filter only to those pixels along block boundaries. A similar technique by Tzou [22] applies a separable anisotropic Gaussian filter, such that the primary axis of the filter is always perpendicular to the block boundary. A space-variant filter that adapts to local characteristics of the signal is proposed by Ramamurthi and Gersho in [23].…”

Section: Introductionmentioning

confidence: 99%

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Blocking artifact detection and reduction in compressed data

Triantafyllidis

Tzovaras

Strintzis

2002

IEEE Trans. Circuits Syst. Video Technol.

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Abstract-A novel frequency-domain technique for image blocking artifact detection and reduction is presented in this paper. The algorithm first detects the regions of the image which present visible blocking artifacts. This detection is performed in the frequency domain and uses the estimated relative quantization error calculated when the discrete cosine transform (DCT) coefficients are modeled by a Laplacian probability function. Then, for each block affected by blocking artifacts, its dc and ac coefficients are recalculated for artifact reduction. To achieve this, a closed-form representation of the optimal correction of the DCT coefficients is produced by minimizing a novel enhanced form of the mean squared difference of slope for every frequency separately. This correction of each DCT coefficient depends on the eight neighboring coefficients in the subband-like representation of the DCT transform and is constrained by the quantization upper and lower bound. Experimental results illustrating the performance of the proposed method are presented and evaluated.

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Section: Reduction Of Blocking Artifact In the Frequency Domainmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Blocking artifact detection and reduction in compressed data

Triantafyllidis

Tzovaras

Strintzis

2002

IEEE Trans. Circuits Syst. Video Technol.

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“…One of the traditional approaches to removing the blocking effect is low-pass post-filtering which was proposed by KouHu Tzou [2]. In this approach, an anisotropic low-pass filtering is carried out only on the boundary pixels to remove the high frequency part of the visible edges caused by the blocking effect.…”

Section: Traditional Approachesmentioning

confidence: 99%

“…Since the blocking effect is primarily due to the inability of the DCT to exploit inter block correlations, most of the above approaches exploit correlations of intensity values in neighboring blocks. The low-pass filtering approach, which reduces high frequency components near the block boundary, has the advantage that it does not require any additional information to be transmitted or any additional operation on the coder side [l], [2]. The biggest drawback to this approach, which is common to most low-pass filtering approaches, is unnecessary blumng of the image.…”

Section: Introduction Iscrete Cosine Transform (Dct) Is Among the mentioning

confidence: 99%

“…To cope with the blockiness problem without increasing the bit rate, the following approaches have been proposed: (a) Low-Pass filtering on boundary pixels [ 11, [2]; (b) DPCM-DC approach [3], [4]; (c) AC prediction using neighboring block DC coefficients [3], [4]. Since the blocking effect is primarily due to the inability of the DCT to exploit inter block correlations, most of the above approaches exploit correlations of intensity values in neighboring blocks.…”

Section: Introduction Iscrete Cosine Transform (Dct) Is Among the mentioning

confidence: 99%

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An optimization approach for removing blocking effects in transform coding

Minami

Zakhor

1995

IEEE Trans. Circuits Syst. Video Technol.

171

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Abstract-One of the drawbacks of the Discrete Cosine Transform (DCT) is visible block boundaries due to coarse quantization of the coefficients. Most restoration techniques for the removing blocking effect are variations of low-pass filtering, and as such, result in unnecessary blurring of the image. In this paper, we propose a new approach for reducing the blocking effect which can be applied to conventional transform coding, such as JPEG standardized coding, without introducing additional information or significant blurring. Our technique exploits the correlation between the intensity values of boundary pixels of two neighboring blocks. Specifically, it is based on the theoretical and empirical observation that under mild assumptions, quantization of the DCT coefficients of two neighboring blocks increases the expected value of the Mean Squared Difference of Slope (MSDS) between the slope across two adjacent blocks, and the average between the boundary slopes of each of the two blocks. The amount of this increase is dependent upon the width of quantization intervals of the transform coefficients. Therefore, among all permissible inverse quantized coefficients, the set which reduces the expected value of this MSDS by an appropriate amount is most likely to decrease the blocking effect. To estimate the set of unquantized coefficients, we solve a constrained quadratic programming problem in which the quantization decision intervals provide upper and lower bound constraints on the coefficients. Our approach is based on the gradient projection method which is motivated by the ordinary method of steepest descent for unconstrained problems. Computer simulations are used to evaluate the performance of the proposed technique. We have shown that from a subjective viewpoint, the blocking effect is less noticeable in our processed images than in the ones using existing filtering techniques.

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Adaptive processing with quadratic programming and LPF for reducing blocking artifacts in DCT image coding

Fukuda

Kawanaka

2000

Electron. Comm. Jpn. Pt. III

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In many image coding methods, the discrete cosine transform (DCT) is used. When the compression ratio is increased, blocking artifacts are generated in the reconstructed image due to quantization error. To resolve this problem, a method is proposed to adaptively change the suppression process of distortion depending on the block. In this method, each block is classified into (1) the flat part where the pel values change monotonically by the value of the received DCT coefficient and (2) the dynamic part. In the block in the flat part, the DCT coefficients are estimated within the quantization width by the quadratic programming method, and the block is regenerated by replacing the received coefficients. The continuity at the block boundary and the boundary pel values after smoothing are used as the objective function. Higher‐order DCT coefficients can be estimated successively. In the region where the variation of the pel values is substantial, human visual sensitivity is not sufficient for the distortion. Therefore, the block boundary is smoothed with a low‐pass filter (LPF) in the block in the variable part. This method is used for processing of several images. It is demonstrated that the SNR is better than those in the JPEG reconstruction method, ac coefficient prediction method, and the LPF method. Overall, a high‐quality reconstructed image is obtained with the blocking artifacts are suppressed. © 2000 Scripta Technica, Electron Comm Jpn Pt 3, 84(4): 50–59, 2001

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Post-Filtering Of Transforms-Coded Images

Cited by 21 publications

References 0 publications

Blocking artifact detection and reduction in compressed data

Blocking artifact detection and reduction in compressed data

An optimization approach for removing blocking effects in transform coding

Adaptive processing with quadratic programming and LPF for reducing blocking artifacts in DCT image coding

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