1,213 research outputs found
Lossless Astronomical Image Compression and the Effects of Noise
We compare a variety of lossless image compression methods on a large sample
of astronomical images and show how the compression ratios and speeds of the
algorithms are affected by the amount of noise in the images. In the ideal case
where the image pixel values have a random Gaussian distribution, the
equivalent number of uncompressible noise bits per pixel is given by Nbits
=log2(sigma * sqrt(12)) and the lossless compression ratio is given by R =
BITPIX / Nbits + K where BITPIX is the bit length of the pixel values and K is
a measure of the efficiency of the compression algorithm.
We perform image compression tests on a large sample of integer astronomical
CCD images using the GZIP compression program and using a newer FITS
tiled-image compression method that currently supports 4 compression
algorithms: Rice, Hcompress, PLIO, and GZIP. Overall, the Rice compression
algorithm strikes the best balance of compression and computational efficiency;
it is 2--3 times faster and produces about 1.4 times greater compression than
GZIP. The Rice algorithm produces 75%--90% (depending on the amount of noise in
the image) as much compression as an ideal algorithm with K = 0.
The image compression and uncompression utility programs used in this study
(called fpack and funpack) are publicly available from the HEASARC web site. A
simple command-line interface may be used to compress or uncompress any FITS
image file.Comment: 20 pages, 9 figures, to be published in PAS
Optimal Compression of Floating-point Astronomical Images Without Significant Loss of Information
We describe a compression method for floating-point astronomical images that
gives compression ratios of 6 -- 10 while still preserving the scientifically
important information in the image. The pixel values are first preprocessed by
quantizing them into scaled integer intensity levels, which removes some of the
uncompressible noise in the image. The integers are then losslessly compressed
using the fast and efficient Rice algorithm and stored in a portable FITS
format file. Quantizing an image more coarsely gives greater image compression,
but it also increases the noise and degrades the precision of the photometric
and astrometric measurements in the quantized image. Dithering the pixel values
during the quantization process can greatly improve the precision of
measurements in the images. This is especially important if the analysis
algorithm relies on the mode or the median which would be similarly quantized
if the pixel values are not dithered. We perform a series of experiments on
both synthetic and real astronomical CCD images to quantitatively demonstrate
that the magnitudes and positions of stars in the quantized images can be
measured with the predicted amount of precision. In order to encourage wider
use of these image compression methods, we have made available a pair of
general-purpose image compression programs, called fpack and funpack, which can
be used to compress any FITS format image.Comment: Accepted PAS
Development of the FITS tools package for multiple software environments
The HEASARC is developing a package of general purpose software for analyzing data files in FITS format. This paper describes the design philosophy which makes the software both machine-independent (it runs on VAXs, Suns, and DEC-stations) and software environment-independent. Currently the software can be compiled and linked to produce IRAF tasks, or alternatively, the same source code can be used to generate stand-alone tasks using one of two implementations of a user-parameter interface library. The machine independence of the software is achieved by writing the source code in ANSI standard Fortran or C, using the machine-independent FITSIO subroutine interface for all data file I/O, and using a standard user-parameter subroutine interface for all user I/O. The latter interface is based on the Fortran IRAF Parameter File interface developed at STScI. The IRAF tasks are built by linking to the IRAF implementation of this parameter interface library. Two other implementations of this parameter interface library, which have no IRAF dependencies, are now available which can be used to generate stand-alone executable tasks. These stand-alone tasks can simply be executed from the machine operating system prompt either by supplying all the task parameters on the command line or by entering the task name after which the user will be prompted for any required parameters. A first release of this FTOOLS package is now publicly available. The currently available tasks are described, along with instructions on how to obtain a copy of the software
Comparison of chromogenic media for recovery of carbapenemase-producing enterobacteriaceae (CPE) and evaluation of CPE prevalence at a tertiary care academic medical center
We evaluated the performance characteristics of chromID CARBA and HardyCHROM Carbapenemase for the detection of carbapenemase-producing Enterobacteriaceae (CPE). A CPE prevalence study was conducted using chromID CARBA; this demonstrated that in low-prevalence settings, CPE screening agars may lack specificity, and confirmation of putative isolates is necessary
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Irreconcilable differences : modernist representations of class and gender in the early work (1911-1936) of Rebecca West
This thesis on Rebecca West's writing (1911-1936) addresses the relationship between her polemical essays and her fiction, exploring modernist representations of class and gender differences and conflicts. West expresses a view of gender and class relations in early twentieth century Great Britain that is based on opposed and dichotomous pairs which cannot be deconstructed. Multiple and shifting tensions between socially constructed versus essentialist views emerge through representations of war, marriage, female bodies, and social bodies. I provide an analysis of several of West's political articles published in The Clarion and in The New Republic from 19/1-/916, and two novels, The Return of the Soldier (1918) and The Thinking Reed (1936). I argue for a reading of West's work that does not attempt to reconcile the contradictions therein, but rather examines them as "irreconcilable differences." Reading West's work in this way allows for an understanding of West's view of the paradoxical nature of gender and class relations, as well as what Marshall Berman termed the "paradoxical unity" of modernism
DDR2 controls breast tumor stiffness and metastasis by regulating integrin mediated mechanotransduction in CAFs
Biomechanical changes in the tumor microenvironment influence tumor progression and metastases. Collagen content and fiber organization within the tumor stroma are major contributors to biomechanical changes (e., tumor stiffness) and correlated with tumor aggressiveness and outcome. What signals and in what cells control collagen organization within the tumors, and how, is not fully understood. We show in mouse breast tumors that the action of the collagen receptor DDR2 in CAFs controls tumor stiffness by reorganizing collagen fibers specifically at the tumor-stromal boundary. These changes were associated with lung metastases. The action of DDR2 in mouse and human CAFs, and tumors in vivo, was found to influence mechanotransduction by controlling full collagen-binding integrin activation via Rap1-mediated Talin1 and Kindlin2 recruitment. The action of DDR2 in tumor CAFs is thus critical for remodeling collagen fibers at the tumor-stromal boundary to generate a physically permissive tumor microenvironment for tumor cell invasion and metastases
PHOTZIP: A Lossy FITS Image Compression Algorithm that Protects User-Defined Levels of Photometric Integrity
A lossy compression algorithm is presented for astronomical images that
protects photometric integrity for detected point sources at a user-defined
level of statistical tolerance. PHOTZIP works by modeling, smoothing, and then
compressing the astronomical background behind self-detected point sources,
while completely preserving values in and around those sources. The algorithm
also guaranties a maximum absolute difference (in terms of ) between
each compressed and original background pixel, allowing users to control
quality and lossiness. For present purposes, PHOTZIP has been tailored to FITS
format and is freely available over the web. PHOTOZIP has been tested over a
broad range of astronomical imagery and is in routine use by the Night Sky Live
(NSL) project for compression of all-sky FITS images. Compression factors
depend on source densities, but for the canonical NSL implementation, a PHOTZIP
(and subsequently GZIP or BZIP2) compressed file is typically 20% of its
uncompressed size.Comment: 10 pages, 3 figures. Accepted for publication in A
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