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PubMed2004

Design of vector quantizer for image compression using self-organizing feature map and surface fitting.

We propose a new scheme of designing a vector quantizer for image compression. First, a set of codevectors is generated using the self-organizing feature map algorithm. Then, the set of blocks associated with each code vector is modeled by a cubic surface for better perceptual fidelity of the reconstructed images. Mean-removed vectors from a set of training images is used for the construction of a generic codebook. Further, Huffman coding of the indices generated by the encoder and the difference-coded mean values of the blocks are used to achieve better compression ratio. We proposed two indices for quantitative assessment of the psychovisual quality (blocking effect) of the reconstructed image. Our experiments on several training and test images demonstrate that the proposed scheme can produce reconstructed images of good quality while achieving compression at low bit rates. Index Terms-Cubic surface fitting, generic codebook, image compression, self-organizing feature map, vector quantization.

Algorithms↗
PubMed2004

Evaluation of JPEG 2000 encoder options: human and model observer detection of variable signals in X-ray coronary angiograms.

Previous studies have evaluated the effect of the new still image compression standard JPEG 2000 using nontask based image quality metrics, i.e., peak-signal-to-noise-ratio (PSNR) for nonmedical images. In this paper, the effect of JPEG 2000 encoder options was investigated using the performance of human and model observers (nonprewhitening matched filter with an eye filter, square-window Hotelling, Laguerre-Gauss Hotelling and channelized Hotelling model observer) for clinically relevant visual tasks. Two tasks were investigated: the signal known exactly but variable task (SKEV) and the signal known statistically task (SKS). Test images consisted of real X-ray coronary angiograms with simulated filling defects (signals) inserted in one of the four simulated arteries. The signals varied in size and shape. Experimental results indicated that the dependence of task performance on the JPEG 2000 encoder options was similar for all model and human observers. Model observer performance in the more tractable and computationally economic SKEV task can be used to reliably estimate performance in the complex but clinically more realistic SKS task. JPEG 2000 encoder settings different from the default ones resulted in greatly improved model and human observer performance in the studied clinically relevant visual tasks using real angiography backgrounds.

Algorithms↗
PubMedDate not supplied

MRI of intracranial neurovascular compression.

Twelve patients with clinical indications of intracranial neurovascular compression (6, hemifacial spasm; 4, trigeminal neuralgia; 2, vertigo and tinnitus) were studied by MRI. Axial 1 mm thick slices were obtained in a 1.5 T unit using a three-dimensional (3D) fast low angle shot data set of 32 contiguous slices. The data were post-processed with multiplanar reconstruction algorithms to obtain oblique sagittal (along the long axis of a nerve) images or coronal images with a slice thickness of 0.8 mm. The MR angiographic images were also obtained from the same 3D data set with maximum intensity projection algorithms. The MR studies showed that 9 of 12 patients had neurovascular compression caused by one or two arteries. These findings were verified at surgery. In two of the remaining three patients, MRI failed to delineate the affected nerves compressed by a vein in one, and a previously applied prosthesis in the other. In the last patient no neurovascular compression was found by MRI or at surgery.

Aged↗
PubMed1999

Noise-resilient estimation of optical flow by use of overlapped basis functions.

Conventional techniques for the computation of optical flow from image gradients are used to formulate the problem as a nonlinear optimization that comprises a gradient constraint term and a field smoothness factor. The results of these techniques are often erroneous, highly sensitive to noise and numerical precision, determined sparsely, and computationally expensive. We regularize the gradient constraint equation by modeling optical flow as a linear combination of a set of overlapped basis functions. We develop a theory for estimating model parameters robustly and reliably. We prove that the extended-least-squares solution proposed here is unbiased and robust to small perturbations in the gradient estimates and to mild deviations from the gradient constraint. Our solution is obtained with a numerically stable sparse matrix inversion, which gives a reliable flow-field estimate over the entire frame. To validate our claims, we perform a series of experiments on standard benchmark data sets at a range of noise levels. Overall, our algorithm outperforms by a wide margin the others considered in the comparison. We demonstrate the applicability of our algorithm to image mosaicking and to motion superresolution through experiments on noisy compressed sequences. We conclude that our flow-field model offers greater accuracy and robustness than conventional optical flow techniques in a variety of situations and permits real-time operation.

Algorithms↗
PubMed2006

Light field compression using disparity-compensated lifting and shape adaptation.

We propose disparity-compensated lifting for wavelet compression of light fields. With this approach, we obtain the benefits of wavelet coding, such as scalability in all dimensions, as well as superior compression performance. Additionally, the proposed approach solves the irreversibility limitations of previous light field wavelet coding approaches, using the lifting structure. Our scheme incorporates disparity compensation into the lifting structure for the transform across the views in the light field data set. Another transform is performed to exploit the coherence among neighboring pixels, followed by a modified SPIHT coder and rate-distortion optimized bitstream assembly. A view-sequencing algorithm is developed to organize the views for encoding. For light fields of an object, we propose to use shape adaptation to improve the compression efficiency and visual quality of the images. The necessary shape information is efficiently coded based on prediction from the existing geometry model. Experimental results show that the proposed scheme exhibits superior compression performance over existing light field compression techniques.

Algorithms↗
PubMed2000

Ultrasound grayscale image compression with JPEG and wavelet techniques.

The purpose of the study was to evaluate the effects of lossy compression on grayscale ultrasound images to determine how much compression can be applied while still maintaining images that are acceptable for diagnostic purposes. The study considered how the acquisition technique (video frame-grabber versus directly acquired in digital form) influences how much compression can be applied. For directly acquired digital images, the study considered how text (that is burned into the image) affects the compressibility of the image. The lossy compression techniques that were considered include JPEG and a Wavelet algorithm using set partitioning in hierarchical trees (SPIHT).

Image Processing, Computer-Assisted↗
PubMed1993

Vector quantization distortion of medical ultrasound features.

Pruned-tree structured vectored quantization (PTSVQ) was applied to the lower five gray scale remapped bits of normal and fatty ultrasound liver images. The upper bits were compressed reversibly. This combination of techniques is termed PTSVQ with splitting. The effect of the compression on the difference in texture between normal and fatty liver images was studied at different compression rates and distortions. The changes in texture were measured by changes in the principal components of the covariance matrix of image vectors. The vectors were the same size as those used in the compression technique. There were clear differences in the components of normal and fatty liver images. These differences were largely removed by the PTSVQ with splitting technique even at average single pixel distortions several times smaller than the image noise. These results suggest that the effect of compression on second order statistics should be measured when evaluating algorithms in addition to the first order average distortion.

Fatty Liver↗
PubMed1993

Corticosteroid supplementation during cardiac arrest in rats.

HYPOTHESIS: Corticosteroids will improve the rate of resuscitation from cardiac arrest. DESIGN: Prospective blinded randomized placebo-controlled trial. INTERVENTION: An 8-min cardiac arrest was induced by KCl infusion and chest restriction in 36 male Sprague-Dawley rats with continuous EKG and arterial blood pressure monitoring. At the start of CPR the rats received one of three study drugs: normal saline (placebo); 0.05 mg hydrocortisone (Group A) and 0.25 mg hydrocortisone (Group B). Mechanical ventilation, chest compressions and ACLS drug administration were provided following a standardized algorithm. RESULTS: The resuscitation rate was significantly higher (P < 0.05) in Group B (92%) compared to Group A (50%) and placebo (50%). For the rats resuscitated, the duration of CPR (placebo = 163 s, Group A = 126 s, Group B = 120 s) and the amount of epinephrine used (placebo = 0.007 mg, Group A = 0.005 mg, Group B = 0.005 mg) did not reach statistical significance (P = 0.15 and P = 0.21). CONCLUSION: Hydrocortisone significantly increased the rate of ROSC from cardiac arrest. There also appears to be a trend of decreasing duration of CPR and epinephrine requirements with hydrocortisone. Further studies evaluating the mechanism of action and long term effects of hydrocortisone in cardiac arrest need to be conducted.

Animals↗
PubMed2004

Cyclic loading moves the peak stress to the cartilage surface in a biphasic model with isotropic solid phase properties.

Experimental indentation studies of articular cartilage have shown the initiation of fibrillation at the cartilage surface. To date, isotropic biphasic models have failed to support this observation. This study presents the results of applying cyclic loading to an isotropic biphasic cartilage indentation model using an FE based solution procedure. The model incorporated a contact dependent flow algorithm to prevent fluid movement across contacting regions. The results show that under the application of cyclic loading the location of key peak solid phase stresses move from the base of the cartilage layer to the surface and thus to the region of experimentally observed cartilage surface failures.

Algorithms↗
PubMed2002

Three-dimensional simulation of fracture repair in the human tibia.

Finite element models of bones can be generated based on images obtained non-invasively in the clinic. One area where such models may prove useful is in the assessment of fracture healing of long bones. To establish the feasibility of such a proposal, a three dimensional finite element model of a fractured tibia was generated, and a model of tissue differentiation and bone regeneration was used to simulate the progress of healing under two different loading magnitudes. Healing is successful under the lower load and unsuccessful under the higher load--this proves that the model has the potential to identify loads that would cause healing to fail. Following a proposal by Richardson et al. [J. Bone Jt Surg. Vol. 76B (1994) pp. 389-394] that the bending stiffness can be used to assess the extent of healing, the bending stiffness was computed during healing--it was shown that the stiffness changed in a similar manner that observed clinically. In conclusion, the paper establishes that 3D computer simulation could be a tool for assessment of the fracture healing under different orthopedic treatments.

Algorithms↗
PubMed2004

Space-conserving optimal DNA-protein alignment.

DNA-protein alignment algorithms can be used to discover coding sequences in a genomic sequence, if the corresponding protein derivatives are known. They can also be used to identify potential coding sequences of a newly sequenced genome, by using proteins from related species. Previously known algorithms either solve a simplified formulation, or sacrifice optimality to achieve practical implementation. In this paper, we present a comprehensive formulation of the DNA-protein alignment problem, and an algorithm to compute the optimal alignment in O(mn) time using only four tables of size (m + 1) x (n + 1), where m and n are the lengths of the DNA and protein sequences, respectively. We also developed a Protein and DNA Alignment program PanDA that implements the proposed solution. Experimental results indicate that our algorithm produces high quality alignments.

Algorithms↗
PubMed2005

Beat-based ECG compression using gain-shape vector quantization.

An electrocardiogram (ECG) data compression scheme is presented using the gain-shape vector quantization. The proposed approach utilizes the fact that ECG signals generally show redundancy among adjacent heartbeats and adjacent samples. An ECG signal is QRS detected and segmented according to the detected fiducial points. The segmented heartbeats are vector quantized, and the residual signals are calculated and encoded using the AREA algorithm. The experimental results show that with the proposed method both visual quality and the objective quality are excellent even in low bit rates. An average PRD of 5.97% at 127 b/s is obtained for the entire 48 records in the MIT-BIH database. The proposed method also outperforms others for the same test dataset.

Algorithms↗
PubMed2005

Rate-distortion optimal video summary generation.

The need for video summarization originates primarily from a viewing time constraint. A shorter version of the original video sequence is desirable in a number of applications. Clearly, a shorter version is also necessary in applications where storage, communication bandwidth, and/or power are limited. The summarization process inevitably introduces distortion. The amount of summarization distortion is related to its "conciseness," or the number of frames available in the summary. If there are m frames in the original sequence and n frames in the summary, we define the summarization rate as m/n, to characterize this "conciseness". We also develop a new summarization distortion metric and formulate the summarization problem as a rate-distortion optimization problem. Optimal algorithms based on dynamic programming are presented and compared experimentally with heuristic algorithms. Practical constraints, like the maximum number of frames that can be skipped, are also considered in the formulation and solution of the problem.

Algorithms↗
PubMed2006

JPEG2000 encoding with perceptual distortion control.

In this paper, a new encoding approach is proposed to control the JPEG2000 encoding in order to reach a desired perceptual quality. The new method is based on a vision model that incorporates various masking effects of human visual perception and a perceptual distortion metric that takes spatial and spectral summation of individual quantization errors into account. Compared with the conventional rate-based distortion minimization JPEG2000 encoding, the new method provides a way to generate consistent quality images at a lower bit rate.

Algorithms↗
PubMed2006

Source-optimized irregular repeat accumulate codes with inherent unequal error protection capabilities and their application to scalable image transmission.

The common practice for achieving unequal error protection (UEP) in scalable multimedia communication systems is to design rate-compatible punctured channel codes before computing the UEP rate assignments. This paper proposes a new approach to designing powerful irregular repeat accumulate (IRA) codes that are optimized for the multimedia source and to exploiting the inherent irregularity in IRA codes for UEP. Using the end-to-end distortion due to the first error bit in channel decoding as the cost function, which is readily given by the operational distortion-rate function of embedded source codes, we incorporate this cost function into the channel code design process via density evolution and obtain IRA codes that minimize the average cost function instead of the usual probability of error. Because the resulting IRA codes have inherent UEP capabilities due to irregularity, the new IRA code design effectively integrates channel code optimization and UEP rate assignments, resulting in source-optimized channel coding or joint source-channel coding. We simulate our source-optimized IRA codes for transporting SPIHT-coded images over a binary symmetric channel with crossover probability p. When p = 0.03 and the channel code length is long (e.g., with one codeword for the whole 512 x 512 image), we are able to operate at only 9.38% away from the channel capacity with code length 132380 bits, achieving the best published results in terms of average peak signal-to-noise ratio (PSNR). Compared to conventional IRA code design (that minimizes the probability of error) with the same code rate, the performance gain in average PSNR from using our proposed source-optimized IRA code design is 0.8759 dB when p = 0.1 and the code length is 12800 bits. As predicted by Shannon's separation principle, we observe that this performance gain diminishes as the code length increases.

Algorithms↗
PubMed2006

Drift-resistant SNR scalable video coding.

We address the problem of enhancement layer drift estimation for fine granular scalable video. An optimal per-pixel drift estimation algorithm is introduced. The encoder assumes that there is some truncation of the enhancement layer, which does not allow the enhancement layer reference to be properly reconstructed, and the encoder recursively estimates the associated drift and chooses coding modes accordingly. The approach yields performance gains of about 1 dB across low to medium rates. In addition, we investigate dual frame prediction, for both base and enhancement layer, with pulsed-quality allocation in the base

Algorithms↗
PubMed2006

A technique for producing scalable color-quantized images with error diffusion.

To reliably and efficiently deliver media information to diverse clients over heterogeneous networks, the media involved must be scalable. In this paper, a color quantization algorithm for generating scalable color-indexed images is proposed based on a multiscale error diffusion framework. Images of lower resolutions are embedded in the outputs such that a simple down-sampling process can extract images of any desirable resolutions. Images possessing this scalable property support transmission over the Internet which contains clients with different display resolutions, systems with different caching resources and networks with varying bandwidths and QoS capabilities. Unlike most of the color halftoning algorithms available nowadays, the proposed algorithm is not dedicated for printing applications but for color-indexed displays. It works with any arbitrary palettes of different size.

Algorithms↗