Improvement In Compression Ratio Research Articles

Motion estimation and compensation based on almost shift‐invariant wavelet transform for image sequence coding

There has been rapid progress in the application of wavelet transforms to image and image sequence compression. The standard discrete wavelet transform lacks transition invariance in image decomposition which will affect the accuracy of motion estimation from the decomposed subimages in video coding. In this article, we present a study of applying an almost shift-invariant wavelet transform with “oversampled frames” to image sequence compression. With minimal oversampling and biorthogonal spline wavelets in the almost shift-invariant wavelet transform, motion vectors can be more accurately estimated, contributing toward fewer prediction errors in comparison to those obtained with the standard discrete wavelet transform. Thus, an improved compression ratio can be obtained. We present two new algorithms, the full-motion oversampling algorithm (FMOS) and the reduced search multiresolution motion estimation algorithm (MRME), for estimating motion fields at different scales and in different subimages. In the latter, motion vectors at a higher resolution are approximated by the motion vector estimates at a lower resolution through proper scaling. Experiments were performed on three video sequences with a variety of motions including slow, fast, and zooming. Our results have shown that both algorithms, FMOS and MRME, using the almost shift-invariant oversampled frame wavelet transform have reduced prediction errors and enhanced the compression performance in terms of peak-signal-to-noise ratio (PSNR) for the same bit rate when compared to the existing full motion standard algorithm. © 1998 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 9, 214–229, 1998

Motion estimation and compensation based on almost shift-invariant wavelet transform for image sequence coding

There has been rapid progress in the application of wavelet transforms to image and image sequence compression. The standard discrete wavelet transform lacks transition invariance in image decomposition which will affect the accuracy of motion estimation from the decomposed subimages in video coding. In this article, we present a study of applying an almost shift-invariant wavelet transform with “oversampled frames” to image sequence compression. With minimal oversampling and biorthogonal spline wavelets in the almost shift-invariant wavelet transform, motion vectors can be more accurately estimated, contributing toward fewer prediction errors in comparison to those obtained with the standard discrete wavelet transform. Thus, an improved compression ratio can be obtained. We present two new algorithms, the full-motion oversampling algorithm (FMOS) and the reduced search multiresolution motion estimation algorithm (MRME), for estimating motion fields at different scales and in different subimages. In the latter, motion vectors at a higher resolution are approximated by the motion vector estimates at a lower resolution through proper scaling. Experiments were performed on three video sequences with a variety of motions including slow, fast, and zooming. Our results have shown that both algorithms, FMOS and MRME, using the almost shift-invariant oversampled frame wavelet transform have reduced prediction errors and enhanced the compression performance in terms of peak-signal-to-noise ratio (PSNR) for the same bit rate when compared to the existing full motion standard algorithm. © 1998 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 9, 214–229, 1998

Application of artificial neural networks for spacecraft instrument data compression

This paper describes the use of simple feedforward artificial neural networks for spacecraft instrument data compression. It details simulations performed for compression of data from the CRRES spacecraft's Iowa plasma wave experiment, swept frequency receiver. Compression performance is compared with results obtained using the adaptive cosine transform coding, which will be used to compress data from the Mars 96 Elisma instruments. A compression ratio improvement of over 100% is achieved over adaptive cosine transform coding.

Hybrid predictive/VQ lossless image coding

A multiplicative autoregressive model is used in a lossless predictive image coding scheme. The use of vector quantisation (VQ) for compression of the model coefficients leads to an improved compression ratio. Both image adaptive and universal codebooks are considered. A comparative analysis of the new coder is presented through simulation results.

The transform image codec based on fuzzy control and human visual system

A novel processing scheme for gray level image compression based on the human visual system (HVS) and fuzzy control is proposed. The spatial model of the threshold vision that incorporates the masking processes takes account of two major sensitivities of the human visual system, namely background illumination levels and spatial frequency sensitivities. The distortion measures use common sense fuzzy rules for image quality prediction. The human visual models have been successfully applied in image compression. By the addition of the visual model, performance of these systems has a visible improvement of subject quality depending on visual perception. The processed image performs both improved compression ratio as well as improved SNR (signal to noise ratio) in compression to the standardized still image compression technique, i.e., the JPEG.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

New concepts in turbomolecular pump design

Modern turbopumps were introduced in 1958 and are now widely used in industrial and laboratory applications. At the present time, three types of turbine-type pumps are in existence: axial flow turbomolecular pumps, turbodrag pumps, and hybrid pumps combining the two types on the same axis. Recent emphasis on oil-free vacuum pumping systems has revived the interest in pumps which can tolerate higher discharge pressures. When exit pressures reach 10 mbar (or higher), the well-established molecular flow analysis cannot be used. It appears that the existing turbomolecular and turbodrag pumps, which take their basic design from historical models, are not optimized in regard to their speed and throughput performance. Following a simple concept of bulk velocity variation, which can be used for assessing the density continuum (despite the existence of molecular flow through parts of the pump) an optimized pumping speed and compression staging arrangement was developed which demonstrates a practical improvement in compression ratios of as high as 40 times for light gases (helium and hydrogen), without increasing the size and power, compared to a conventional pump. Turbine-type pumps, unlike oil-vapor jet and high-vacuum cryopumps, permit practical engineering solutions for expanding the pressure regime to almost arbitrary high pressure. This makes it possible to use oil-free backing pumps at intermediate pressures of 10–100 mbar using relatively small changes in design.

Fast and efficient variable-to-fixed-length coding algorithm

Variable-to-fixed-length coding implementations, according to the Tunstall algorithm, are shown to be significantly less complex than fixed-to-variable-length coding schemes such as the Huffman scheme. A modified version of Tunstall coding is presented, with improved compression ratio.

Compression ratio and leakage through stages in turbomolecular pumps

The presence of leaks through the stages of a turbomolecular pump affects its actual compression ratio. The measured compression ratios are in many instances much lower than calculated ones if this effect is not considered in the calculation. A theoretical evaluation is done for the effect of the leakage from high pressure stages to the low pressure stages. A simple model is developed to calculate the decrease in the compression ratio caused by leakage. Two cases are studied in detail, referring to a particular design of the pump: (1) the conductance in the region between the envelope of the pump and the spacer rings is much larger than the conductance between two adjacent spacer rings; (2) the conductance between two adjacent spacer rings is much larger than the conductance in the region between the envelope of the pump and the spacer rings. In the latter case, compression ratios might be very close to the maximum (without leakage). Above considerations show a way to improve compression ratios in turbomolecular pumps. Finally an experimental verification has been performed, the calculated configurations have been tested, and the experimental and theoretical results are compared.

Present Status of Formoder

Formoder, short for Formant-Moment Coder, is a system which utilizes slowly varying parameters and discrete linguistic features extracted from the speech spectrum for speech band-width compression. Formoder offers a different approach than Vocoder for the approximation of the speech spectrum by using FM as well as AM parameters. In addition, the use of certain linguistic features limits the dynamic ranges needed in the analyzer and synthesizer components. The system falls short of the ideal representation of a time varying dynamic model of the speech mechanism, but it holds promise for an improvement in compression ratio over that of Vocoder. This is perhaps the reason for continued study of essentially similar systems in various laboratories. This paper is intended to discuss further the above-mentioned points and will describe the present status of Formoder together with system evaluation and articulation tests. In a typical operation of the system using two formants and one moment, articulation tests show the Harvard PB word lists score over 40% and sentence score over 80%. [The research in this paper has been made possible through support and sponsorship extended by the Electronics Research Directorate of the Air Force Cambridge Research Center, under Contract AF19(604)-1039, Item I, and AF19 (604)-2198.]