Reversible decorrelation method for progressive transmission of 3-Dmedical image

In this paper, the authors present a new reversible decorrelation method of three-dimensional (3-D) medical images for progressive transmission. Progressive transmission of an image permits gradual improvement of image quality while being displayed. When the amount of image data is very large, as a 3-D medical image, the progressive transmission plays an important role in viewing or browsing the image. The data structure presented in this paper takes account of interframe correlation as well as intraframe correlation of the 3-D image. This type of data structure has been termed the 3-D hierarchy embedded differential image (3-D-HEDI) as was derived from the earlier HEDI structure (Kim et al., 1995). Experiments were conducted to verify the performance of 3-D HEDI in terms of the decorrelation efficiency as well as the progressive transmission efficiency. It is compared with those of conventional hierarchy interpolation (HINT), two-dimensional (2-D) HEDI and differential pulse code modulation (DPCM). Experimental results indicate that 3-D HEDI outperforms HINT, 2-D HEDI and DPCM in both decorrelation efficiency as well as the progressive transmission efficiency on 3-D medical images     

A Lossless Compression Method for Medical Image Sequences Using JPEG-LS and Interframe Coding

Hospitals and medical centers produce an enormous amount of digital medical images every day, especially in the form of image sequences, which requires considerable storage space. One solution could be the application of lossless compression. Among available methods, JPEG-LS has excellent coding performance. However, it only compresses a single picture with intracoding and does not utilize the interframe correlation among pictures. Therefore, this paper proposes a method that combines the JPEG-LS and an interframe coding with motion vectors to enhance the compression performance of using JPEG-LS alone. Since the interframe correlation between two adjacent images in a medical image sequence is usually not as high as that in a general video image sequence, the interframe coding is activated only when the interframe correlation is high enough. With six capsule endoscope image sequences under test, the proposed method achieves average compression gains of 13.3% and 26.3 % over the methods of using JPEG-LS and JPEG2000 alone, respectively. Similarly, for an MRI image sequence, coding gains of 77.5% and 86.5% are correspondingly obtained.     

Reversible intraframe compression of medical images

The performance of several reversible, intraframe compression methods is compared by applying them to angiographic and magnetic resonance (MR) images. Reversible data compression involves two consecutive steps: decorrelation and coding. The result of the decorrelation step is presented in terms of entropy. Because Huffman coding generally approximates these entropy measures within a few percent, coding has not been investigated separately. It appears that a hierarchical decorrelation method based on interpolation (HINT) outperforms all other methods considered. The compression ratio is around 3 for angiographic images of 8-9 b/pixel, but is considerably less for MR images whose noise level is substantially higher.     

Motion differential set partition coding for image sequence and video compression

Efficient image sequence coding exploits both intra- and inter-frame correlations. Set partition coding (SPC) is efficient in intra-frame de-correlation for still images. Based on SPC, a novel image sequence coding system, called motion differential SPC (M-D-SPC), is presented in this paper. It removes inter-frame redundancy by re-using the significance map of a previously SPC coded frame. Every frame is encoded and decoded separate from other frames. Furthermore, there is no reconstruction of encoded frames in the encoder, as is done with interframe prediction methods. The M-D-SPC exhibits an auxiliary key frame coding framework, which achieves higher coding efficiency compared to the all-intra-coding schemes and meanwhile maintains the beneficial features of SPC all-intra-coding, such as computational simplicity, rate scalability, error non-propagation, and random frame access. SPIHT-based simulations on hyperspectral images, 3D/4D medical images, and video show greater compression efficiency than the standard intraframe coding method of motion JPEG2000.     

Hybrid coders with motion compensation

This paper investigates analytically the effects of motion compensation in a coder based on the observed properties of motion-compensated frame difference (MCFD) signals. The AR(1) processes with a given pixel-to-pixel autocorrelation coefficient will be used to model the intraframe images. For interframe motion, each image is allowed to have both moving and nonmoving parts, with the moving parts executing a range of translational motion. From this mathematical model, the statistical characteristics of MCFD signals are derived. Motion compensation gain, 2-D intraframe transform gain, and hybrid gain are next evaluated to ascertain their suitability for the coding process. Experimental results on the Trevor sequence seem to confirm the model and conform with its analytical results.     

Efficient multiframe Wiener restoration of blurred and noisy imagesequences

Computationally efficient multiframe Wiener filtering algorithms that account for both intraframe (spatial) and interframe (temporal) correlations are proposed for restoring image sequences that are degraded by both blur and noise. One is a general computationally efficient multiframe filter, the cross-correlated multiframe (CCMF) Wiener filter, which directly utilizes the power and cross power spectra of only NxN matrices, where N is the number of frames used in the restoration. In certain special cases the CCMF lends itself to a closed-form solution that does not involve any matrix inversion. A special case is the motion-compensated multiframe (MCMF) filter, where each frame is assumed to be a globally shifted version of the previous frame. In this case, the interframe correlations can be implicitly accounted for using the estimated motion information. Thus the MCMF filter requires neither explicit estimation of cross correlations among the frames nor matrix inversion. Performance and robustness results are given.     

Very low bit-rate video coding with DFD segmentation

A video coding system for applications requiring very low bit-rate is presented. This coding scheme uses an intraframe coder for the initial frame in the video sequence and subsequent frames are coded using an interframe coding method. A wavelet-based technique is used for intraframe coding. For interframe coding, displaced frame differences (DFD) are computed and coded using a segmentation-based method wherein the displaced frame difference is segmented into active and inactive regions using morphological operators. To meet the very low bit-rate requirements, the motion vectors are processed so as to reduce their contribution to the overall bit-rate. To reduce coding artifacts, a post-processing technique is developed for use at the decoder. Coding performance of the proposed coding scheme is evaluated at 16 kbit/s and 32 kbit/s using luminance component of several typical test sequences at QCIF resolution with a frame rate 8.3 frame/s.     

The use of contextual information in the reversible compression of medical images

The authors investigate the use of conditioning events (or contexts) in improving the performances of known compression methods by building a source model with multiple contexts to code the decorrelated pixels. Three methods for reversible compression, namely DPCM (differential pulse code modulation), WHT (Walsh-Hadamard transform), and HINT (hierarchical interpolation), employing, respectively, predictive decorrelation, transform decorrelation, and multiresolution decorrelation, are considered. It is shown that the performance of these methods can be enhanced significantly, sometimes even up to 40%, by using contexts. The enhanced DPCM method is found to perform the best for MR and UT (ultrasound) medical images; the enhanced WHT method is found to be the best for X-ray images. The source models used in the enhanced models employ several hundred contexts.     

一种基于双正交小波变换和格型矢量量化的视频编码算法

本文提出了基于双正交小波变换（ｂｉｏｒｔｈｏｇｏｎａｌｗａｖｅｌｅｔｔｒａｎｓｆｏｒｍ）和格型矢量量化（ＬＶＱｌａｔｔｉｃｅｖｅｃｔｏｒｑｕａｎｔｉｚａｔｉｏｎ）的视频编码算法。在该方案中，小波变换将图像分解成多分辨率（ｍｕｌｔｉｒｅｓｏｌｕｔｉｏｎ）的子带图像，多分辨率运动估值（ＭＲＭＥ，ｍｕｌｔｉｒｅｓｏｌｕｔｉｏｎｍｏｔｉｏｎｅｓｔｉｍａｔｉｏｎ）技术实现子带图像的帧间预测，格型矢量量化对预测差值子带图像进行编码，从而获得了性能较好的活动图像编码新算法。     

Digital HDTV compression techniques

The roles that digital high-definition television (HDTV) compression techniques play in HDTV applications, such as digital HDTV terrestrial broadcasting, are discussed. Images can be encoded intraframe and/or interframe, depending on the requirement of compression rate and the picture quality. Using source coding, redundancy in the spatial and temporal domains can be greatly reduced while preserving the level of image quality required for the given application     

Reversible 3-D decorrelation of medical images

Two methods, namely, differential pulse code modulation (DPCM) and hierarchical interpolation (HINT), are considered. It is shown that HINT cannot be extended straightforwardly to 3-D images as contrasted with DPCM. A 3-D HINT is therefore proposed which is based on a combination of 2-D and 3-D filters. Both decorrelation methods were applied to three-dimensional computed tomography (CT), magnetic resonance (MR), and single-photon-emission CT (SPECT) images. It was found that a 3-D approach is optimal for some studies, while for other studies 2-D or even 1-D decorrelation performs better. The optimal dimensionality of DPCM is related to the magnitudes of the local correlation coefficients (CCs). However, the nonlocal nature of HINT makes the local correlation coefficients useless as indicators of the dimensionality; a better candidate is the image voxel size. For images with cubic or nearly cubic voxels 3-D HINT is generally optimal. For images in which the slice thickness is large compared to the pixel size a 2-D (intraslice) HINT is best. In general, the increase in efficiency obtained by extending 2-D decorrelation method to 3-D is small.     

A fast quadtree motion segmentation for image sequence coding

A new fast quadtree-based variable size block matching scheme is devised for image sequence coding. The novelty of the method lies in the quadtree-based block matching with significantly less computations. In the proposed method, the computational requirements for matching are largely transferred from the evaluation of the mean absolute difference to the computations of the sum norms of the blocks which can be easily obtained. The fast quadtree decomposition scheme partitions an image frame into uniform motion blocks (larger blocks) and non-uniform motion blocks (small blocks). Standard VQ-based interframe coding is applied to uniform motion blocks while non-uniform blocks are intraframe coded. Implementation of this method shows a significantly lower computational requirement and a good-quality reconstruction of images at low bit-rates.     

The Efficiency of Motion-Compensating Prediction for Hybrid Coding of Video Sequences

Performance bounds for generalized hybrid coding of video sequences with motion-compensating prediction are derived based on rate-distortion theory. It is shown that the spatial power spectrum of the motion-compensated prediction error can be calculated from the signal power spectrum and the displacement estimation error p.d.f.. A spatial Wiener filter can improve the efficiency of motion-compensating prediction. Memoryless encoding of the motion-compensated prediction error and intraframe encoding of the motion-compensated prediction error are compared. An evaluation of the rate-distortion functions for a typical videoconference sampling format shows that for integer pel accuracy of the displacement estimate the additional gain by motion-compensating prediction over pure intraframe coding is limited to ∼ 0.8 bits/sample in moving areas. Required accuracies of the displacement estimate for a gain of motion-compensating interframe coding over intraframe coding are given.     

The Effectiveness and Efficiency of Hybrid Transform/DPCM Interframe Image Coding

We seek to evaluate the efficiency of hybrid transform/ DPCM interframe image coding relative to an optimal scheme that minimizes the mean-squared error in encoding a stationary Gaussian image sequence. The stationary assumption leads us to use the asymptotically optimal discrete Fourier transform (DFT) on the full frame of an image. We encode an actual image sequence with full-frame DFT/DPCM at several rates and compare it to previous interframe coding results with the same sequence. We also encode a single frame at these same rates using a full-frame DFT to demonstrate the inherent coding gains of interframe transform DPCM over intraframe coding. We then generate a pseudorandom image sequence with precise Gauss-Markov statistics and encode it by hybrid full-frame DFT/DPCM at various rates. We compare the signal-to-noise ratios (SNR's) of these reconstructions to the optimal ones calculated from the rate-distortion function. We conclude that in a medium rate range below 1 bit/pel/frame where reconstructions for hybrid transform/ DPCM may be unsatisfactory, there is enough margin for improvement to consider more sophisticated coding schemes.     

Wavelet-based coding of time-varying vector fields of ocean-surface winds

Geoscience applications often produce sizable datasets that are vector-valued and increasingly in need of compression algorithms to reduce storage and transmission burdens, particularly when the data are time-varying. In this paper, several advanced interframe-compression techniques are extended from the traditional realm of natural video to the coding of time-varying vector fields. Although similar to natural video in some respects, time-varying vector-field sequences often possess complex temporal evolution of vector-valued features that are important to the analytic quality of the data yet defy the simple motion models widely employed for natural video. To improve coding performance, motion compensation with reduced resolution is proposed such that motion compensation is applied only at low spatial resolution, while high-resolution information, for which the motion model fails, is intraframe coded with no temporal decorrelation. In empirical results on datasets of ocean-surface winds, this reduced-resolution motion-compensation technique results in significant performance improvement and greater feature preservation.     

Tracking a dynamic set of feature points

We address the problems of tracking a set of feature points over a long sequence of monocular images as well as how to include and track new feature points detected in successive frames. Due to the 3-D movement of the camera, different parts of the images exhibit different image motion. Tracking discrete features can therefore be decomposed into several independent and local problems. Accordingly, we propose a localized feature tracking algorithm. The trajectory of each feature point is described by a 2-D kinematic model. Then to track a feature point, an interframe motion estimation scheme is designed to obtain the estimates of interframe motion parameters. Subsequently, using the estimates of motion parameters, corresponding points are identified to subpixel accuracy. Afterwards, the temporal information is processed to facilitate the tracking scheme. Since different feature points are tracked independently, the algorithm is able to handle the image motion arising from general 3-D camera movements. On the other hand, in addition to tracking feature points detected at the beginning, an efficient way to dynamically include new points extracted in subsequent frames is devised so that the information in a sequence is preserved. Experimental results for several image sequences are also reported.     

Encoding of images based on a lapped orthogonal transform

Traditional block transform image coding systems generate artifacts near block boundaries which degrade low bit rate coded images. To reduce these artifacts, a class of unitary transformations, called lapped orthogonal transforms (LOT), is investigated. The basis function on which the signal is projected are overlapped for adjacent blocks. An example of an LOT optimized in terms of energy compaction is numerically derived, using an augmented Lagrangian optimization algorithm. Using this LOT, intraframe coding experiments for 256×240 pixel images were performed at bit rates between 0.1 and 0.35 bits/pixel. The LOT improved the coded image subjective quality over other transforms. The LOT was also used in interframe full-motion video coding experiments for head and shoulder sequences at 28 and 56 kb/s. Significant improvement resulted at low data rates and if no motion compensation were used. However, the improvement was no longer significant at 56 kb/s with full motion compensation     

基于能量积累和形态重构开的红外图像序列小目标检测方法

对多帧红外序列图像膨胀后累加，去除图像随机噪声，提高目标信噪比。使用重构开等形态学算子并结合红外小目标帧内亮度、空间信息和帧间运动信息，消除背景，提取运动小目标。实验结果证明算法可以有效地自动检测小目标。     

Source coding of speech and video signals

Some digital source coding techniques for speech and video are reviewed. Predictive coding of speech, multipulse and code-excited coders and frequency-domain coders are discussed and compared for the coding of speech signals, and intraframe and still image coding and interframe coding are examined for the coding of image and video signals. The emphasis is on those algorithms that offer high compression while maintaining the perceptual quality of the source signals are discussed. Some algorithms that are general waveform coding algorithms and do not strictly depend on the input source are included     

Multilayer subband-based video coding

A motion compensated interframe subband coding algorithm suitable for a wide range of video coding applications is described. In this approach the spectrum of each frame of video signal is first decomposed into smaller frequency bands where each can then be coded accordingly. For the best performance a combination of hybrid DCT/DPCM (discrete cosine transform/differential pulse code modulation), interframe DPCM, and intraframe PCM was considered. To preserve its hierarchical structure each band is coded independently of higher frequency bands but can share information with the lower bands. A simulation was carried out for HDTV sequences