A two-dimensional (2-D) wavelet-based electrocardiogram (ECG) data compression method is presented which employs a modified set partitioning in hierarchical trees (SPIHT) algorithm. This modified SPIHT algorithm utilizes further the redundancy among medium- and high-frequency subbands of the wavelet coefficients and the proposed 2-D approach utilizes the fact that ECG signals generally show redundancy between adjacent beats and between adjacent samples. An ECG signal is cut and aligned to form a 2-D data array, and then 2-D wavelet transform and the modified SPIHT can be applied. Records selected from the MIT-BIH arrhythmia database are tested. The experimental results show that the proposed method achieves high compression ratio with relatively low distortion and is effective for various kinds of ECG morphologies.

A 2-D ECG compression method based on wavelet transform and modified SPIHT

Transform coding using the discrete cosine transform is one of the most popular techniques for image and video compression. However, at low bit rates, the coded images suffer from severe visual distortions. An innovative approach is proposed that deals with artifacts in JPEG compressed images. Our algorithm addresses all three types of artifacts which are prevalent in JPEG images: blocking, and for edges blurring, and aliasing. We enhance the quality of the image via two stages. First, we remove blocking artifacts via boundary smoothing and guided filtering. Then, we reduce blurring and aliasing around the edges via a local edge-regeneration stage. We compared the proposed algorithm with other modern JPEG artifact-removal algorithms. The results demonstrate that the proposed approach is competitive, and can in many cases outperform, competing algorithms.

https://www.spiedigitallibrary.org/journals/Journal-of-Electronic-Imaging/volume-23/issue-1/013018/Algorithm-for-JPEG-artifact-reduction-via-local-edge-regeneration/10.1117/1.JEI.23.1.013018.pdf

Algorithm for JPEG artifact reduction via local edge regeneration

There is disclosed an apparatus, a method and a computer program for video coding. The apparatus comprises a selector configured for selecting a pixel for prediction; a projection definer configured for determining a projection of said pixel to a set of reference pixels; and a prediction definer configured for selecting one or more reference pixels from said set of reference pixels on the basis of said projection, and using said selected one or more reference pixels to obtain a prediction value for said pixel to be predicted.

An apparatus, a method and a computer program for video coding

Identifying individuals in evidence images, where their faces are covered or obstructed, is a challenging task. In the legal case, United States v. Michael Joseph Pepe (2008), Craft and Kong, who served as expert witnesses, used pigmented skin marks to identify a suspect in evidence images. Their expert opinions were challenged, partially because the blocking artifacts generated by the standard JPEG algorithm adversely affect the visibility of the small skin marks. In addition to this case, a huge amount of JPEG-compressed child pornography is posted online every day. Although many methods have been developed to remove blocking artifacts, they are ineffective for our target application. In this paper, a knowledge-based (KB) approach, which simultaneously removes JPEG blocking artifacts, and recovers skin features, is proposed. Given a training set containing both original and compressed skin images, the relationship between original blocks and compressed blocks can be established. This prior information is used to infer the original blocks of compressed evidence images. A Markov-model-based algorithm and a faster one-pass algorithm were developed to make inference, and a block synthesis algorithm was developed to handle the cases where compressed blocks are not contained in the training set. An indexing mechanism was also proposed to deal with large datasets efficiently. Extensive experiments were conducted on images with different characteristics and compression ratios. Both subjective and objective evaluations demonstrated that the KB approach is more effective than other methods. In summary, the KB approach is capable of removing blocking artifacts to recover useful skin features.

/pdf/using-a-knowledge-based-approach-to-remove-blocking-254zrr76kq.pdf

Using a Knowledge-Based Approach to Remove Blocking Artifacts in Skin Images for Forensic Analysis

No-reference analysis of decoded MPEG images for PSNR estimation and post-processing

Design a deblocking filter with three separate modes in DCT-based coding

Medical images must be compressed before transmission due to bandwidth and storage limitations. The set partitioning in hierar- chical trees (SPIHT) algorithm is an efficient method for lossy and loss- less coding of medical images. We propose some modifications to the SPIHT algorithm. It is based on the idea of the insignificant correlation of wavelet coefficients among medium- and high-frequency subbands. In this scheme, insignificant wavelet coefficients that correspond to the same spatial location in the medium subbands can be used to reduce the redundancy by a combined function proposed in associated with the modified SPIHT. In high-frequency subbands, the modified SPIHT pro- poses a dictator to reduce the interband redundancy. Experimental re- sults indicate that the proposed technique improves the quality of the reconstructed medical image in terms of both the peak signal-to-noise ratio (PSNR) and the perceptual results over JPEG2000 and the original SPIHT at the same bit rate. © 2003 Society of Photo-Optical Instrumentation Engi- neers. (DOI: 10.1117/1.1578645)

High Fidelity Medical Image Compression Based on Modified Set Partitioning in Hierarchical Trees.

Blocking effect is the major drawbacks in DCT-based codec at low bit-rate. An efficient anti-blocking effect algorithm is induced in the DCT domain. The proposed algorithm eases the false edges with low computational complexity. Two operations are suggested to different region according the region feature. One operation applies to the smooth region and the boundary edges become to linear distribution and more gradual. The other operation tries to remove some high frequency DCT component and to make the false edge smoothness but not harm for the image quality. The proposed scheme can take best quality in both objective and subjective metrics. Moreover, the objective metric, Peak Signal-to-Noise Ratio (PSNR), can improve to 0.5 ㏈.

Blocking Artifacts Reduction using Two Modes Shift Block Filter

The enlargement method is a partial technology in many application including medical imaging, satellite imaging, and video applications. Due to the wavelet representation has characteristics of the efficient time-frequency localization and the multi-resolution analysis, the wavelet transforms are suitable for processing the image resolution enhancement. Therefore, this method focuses on wavelet-based image resolution enhancement and proposes a framework of enlargement method. This proposed method is based on the estimation of detail wavelet coefficients at high resolution scales. The method exploits shape function according to wavelet coefficient correlation in a local neighborhood and employs undecimated discrete wavelet transform to estimate the unknown detail coefficients. The simulation results objectivity show that the proposed method is considerably superior to conventional image interpolation techniques.

An Enlargement Method Using Undecimated Wavelet Transform and Shape Function

The blocking effect is the major drawback in discrete cosine
transform (DCT)-based codecs at low bit rates. When a high
compression ratio is required, boundaries between adjacent image
blocks become visible. This kind of degradation probably will affect
the judgment of an end user. In this work, a four-neighboring-block
zero-masking technique is proposed in the DCT frequency domain.
The proposed algorithm uses a shift block within four adjacent DCT
blocks to reduce computational complexity. By slightly modifying
several DCT coefficients in the shift block, the artifacts that result
from quantization and dequantization processes are alleviated. The
simulation results show that both visual perception and objective
image quality are noticeably improved.

Ying-Wen Chang

Papers

Design a deblocking filter with three separate modes in DCT-based coding

High Fidelity Medical Image Compression Based on Modified Set Partitioning in Hierarchical Trees.

Blocking Artifacts Reduction using Two Modes Shift Block Filter

An Enlargement Method Using Undecimated Wavelet Transform and Shape Function

Novel artifact removal algorithm in the discrete cosine transform domain