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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Image quality measures and their performance

A number of quality measures are evaluated for gray scale image compression. They are all bivariate exploiting the differences between corresponding pixels in the original and degraded images. It is shown that although some numerical measures correlate well with the observers' response for a given compression technique, they are not reliable for an evaluation across different techniques. The two graphical measures (histograms and Hosaka plots), however, can be used to appropriately specify not only the amount, but also the type of degradation in reconstructed images.

Eskicioglu, Ahmet M.↗
NASA NTRS1984

Characterization of LANDSAT-4 TM and MSS Image Quality for Interpretation of Agricultural and Forest Resources

Systematic analysis of both image and numeric data shows that the overall spectral, spatial, and radiometric quality of the TM data are excellent. Spectral variations in fallow fields are due to the vaiability in soil moisture and surface roughness resulting from the various stages of field preparation for small grains production. Spectrally, the addition of the first TM short wave infrared band (Band 5) significantly enhanced ability to discriminate different crop types. Bands 1, 5, and 6 contain saturated pixels due to high albedo effects, low moisture conditions, and high radiant temperatures of granite and dry, bare soil on south facing slopes, respectively. Spatially, the two fold decrease in interpixel distance and four fold decrease in area per pixel between the TM and MSS allow for improved discrimination of small fields, boundary conditions, road and stream networks in rough terrain, and small forest clearings resulting from various forest management practices.

Degloria, S. D.↗
NASA NTRS1989

Image quality on the Kuiper Airborne Observatory. I - Results of the first flight series

The NASA Kuiper Airborne Observatory (KAO) was flown three times during June and July, 1984 in order to study the causes of the poor seeing obtained with the 0.9-m telescope. High-speed pressure and temperature sensors were placed in the telescope cavity. Several thousand stellar images were recorded under various flight and optical configurations. It is found that the long-exposure image size is affected by telescope tracking errors, imperfect optics, poor optical alignment, telescope and instrument vibration, thermal fluctuations in the telescope cavity, and density fluctuations in the shear layer that forms the boundary between the cavity air and outside air. Possible ways to improve the quality of the images are discussed.

Elliot, J. L.↗
NASA NTRS2008

Dependence of Adaptive Cross-correlation Algorithm Performance on the Extended Scene Image Quality

Recently, we reported an adaptive cross-correlation (ACC) algorithm to estimate with high accuracy the shift as large as several pixels between two extended-scene sub-images captured by a Shack-Hartmann wavefront sensor. It determines the positions of all extended-scene image cells relative to a reference cell in the same frame using an FFT-based iterative image-shifting algorithm. It works with both point-source spot images as well as extended scene images. We have demonstrated previously based on some measured images that the ACC algorithm can determine image shifts with as high an accuracy as 0.01 pixel for shifts as large 3 pixels, and yield similar results for both point source spot images and extended scene images. The shift estimate accuracy of the ACC algorithm depends on illumination level, background, and scene content in addition to the amount of the shift between two image cells. In this paper we investigate how the performance of the ACC algorithm depends on the quality and the frequency content of extended scene images captured by a Shack-Hatmann camera. We also compare the performance of the ACC algorithm with those of several other approaches, and introduce a failsafe criterion for the ACC algorithm-based extended scene Shack-Hatmann sensors.

wave-front sensing and control↗
NASA NTRS1984

Evoluation of Landsat-4 image quality for the interpretation of forest, agricultural and soil resources

Landsat-4 Multispectral Scanner (MSS) and Thematic Mapper (TM) sensor performance is being evaluated through the analysis of images generated by computer-compatible tape data and commercially available film products. Natural targets are used to evaluate spectral variability, spatial resolution, radiometric sensitivity, and geometric fidelity. Spectral characteristics are being evaluated through the interpretation of the image tone and texture variability of known features, while spatial characteristics are evaluated through lineal and areal estimates of similar features and the plotting and analysis of residual errors derived from regressions between relative image coordinates and map coordinates.

Degloria, S. D.↗
NASA NTRS1993

Evaluation of image quality

This presentation outlines in viewgraph format a general approach to the evaluation of display system quality for aviation applications. This approach is based on the assumption that it is possible to develop a model of the display which captures most of the significant properties of the display. The display characteristics should include spatial and temporal resolution, intensity quantizing effects, spatial sampling, delays, etc. The model must be sufficiently well specified to permit generation of stimuli that simulate the output of the display system. The first step in the evaluation of display quality is an analysis of the tasks to be performed using the display. Thus, for example, if a display is used by a pilot during a final approach, the aesthetic aspects of the display may be less relevant than its dynamic characteristics. The opposite task requirements may apply to imaging systems used for displaying navigation charts. Thus, display quality is defined with regard to one or more tasks. Given a set of relevant tasks, there are many ways to approach display evaluation. The range of evaluation approaches includes visual inspection, rapid evaluation, part-task simulation, and full mission simulation. The work described is focused on two complementary approaches to rapid evaluation. The first approach is based on a model of the human visual system. A model of the human visual system is used to predict the performance of the selected tasks. The model-based evaluation approach permits very rapid and inexpensive evaluation of various design decisions. The second rapid evaluation approach employs specifically designed critical tests that embody many important characteristics of actual tasks. These are used in situations where a validated model is not available. These rapid evaluation tests are being implemented in a workstation environment.

Pavel, M.↗
NASA NTRS1985

Characterization of LANDSAT-4 TM and MSS Image Quality for the Interpretation of California's Agricultural Resources

The quality of LANDSAT-4 MSS and TM data was determined by analyzing TM spectral and spatial performance in terms of spectral variability of natural targets and the TM-ground instantaneous field-of-view (IFOV) variability in level and mountainous terrain; and by assessing the suitability of TM and MSS image products for characterizing renewable resourse features. The TM data should be extremelly valuable for crop type and area proportion estimation; undating agricultural land use survey maps at 1:24,000 scale and smaller, field boundary definition; and determining the size and location of individual farmsteads. Ongoing research activities are focused on making spectral and spatial analyses of both MSS and TM analytical film products. The improved spectral, spatial, and radiometric quality of the TM data, should promote a renewed emphasis and interest in direct visual interpretation of these image products, both for updating and improving land stratification in support of resource inventory and for enhancing the image analyst's contribution to computer-assisted analysis procedures.

Degloria, S. D.↗
NASA NTRS1984

Image Quality on the KAO

Three flights of the Kuiper Airborne Observatory (KAO) were taken to study the cause of the point spread function (PSF) degradation. The preliminary conclusions are: (1) the KAO point spread function decreases in size with elapsed time at altitude; (2) image motion is occasionally comparable to the size of the image, but is usually a sub-arcsecond effect; and (3) star images show small scale internal structural changes on a 200 microsecond timescale.

Dunham, E. W.↗
NASA NTRS1982

APQ-102 imaging radar digital image quality study

A modified APQ-102 sidelooking radar collected synthetic aperture radar (SAR) data which was digitized and recorded on wideband magnetic tape. These tapes were then ground processed into computer compatible tapes (CCT's). The CCT's may then be processed into high resolution radar images by software on the CYBER computer.

Griffin, C. R.↗
NASA NTRS2017

Keck Segment Surface Artifacts: Impacts on Segment Phasing and Image Quality

We show that the segments of the Keck telescopes su er from small but signi cant surface artifacts that limit segment phasing accuracy. Both the segment surface artifacts themselves and the limits they place on segment phasing have important implications for adaptive optics, high contrast imaging, and seeing limited observations. These surface artifacts are likely by-products of the segment polishing, most likely the Ion Beam Figuring (IBF) process that constitutes the nal step of the segment surface guring. The surface artifacts di ract a signi cant amount of light out past 3.5 arcseconds and generate chromatic e ects that limit segment phasing accuracy. We present on-sky measurements of the di racted intensity. Segment surface roughness measurements are also presented, which show that surface roughness is not the source of the problem. These results have direct relevance to segment manufacturing for the Thirty Meter Telescope (TMT) and other segmented mirror telescopes.

Brock, Neal↗
NASA NTRS1985

An experimental assessment of the imaging quality of the low energy gamma-ray telescope ZEBRA

One gamma-ray detection plane of the ZEBRA telescope, consisting of nine position sensitive scintillation crystal bars designed to operate over the spectral range 0.2 to 10 MeV, has been constructed in the laboratory. A series of experimental images has been generated using a scaled down flight pattern mask in conjunction with a diverging gamma-ray beam. Point and extended sources have been imaged in order to assess quantitatively the performance of the system.

Butler, R. C.↗
NASA NTRS1995

Software to model AXAF-I image quality

A modular user-friendly computer program for the modeling of grazing-incidence type x-ray optical systems has been developed. This comprehensive computer software GRAZTRACE covers the manipulation of input data, ray tracing with reflectivity and surface deformation effects, convolution with x-ray source shape, and x-ray scattering. The program also includes the capabilities for image analysis, detector scan modeling, and graphical presentation of the results. A number of utilities have been developed to interface the predicted Advanced X-ray Astrophysics Facility-Imaging (AXAF-I) mirror structural and thermal distortions with the ray-trace. This software is written in FORTRAN 77 and runs on a SUN/SPARC station. An interactive command mode version and a batch mode version of the software have been developed.

Ahmad, Anees↗
NASA NTRS1993

Multilayer X-ray mirrors - Interfacial roughness, scattering, and image quality

Scattering of the multilayer coatings used for our normal incidence soft X-ray telescope at a wavelength of 63.5 A has been measured at 1.54 A and grazing angles of incidence and at soft X-rays near normal incidence. Furthermore, the edge of the moon is used as a known test target to estimate the amount of scattering in the arcsec range from images obtained on the date of the solar eclipse on July 11, 1991. The internal surfaces of the coating are inspected by high-resolution electron microscopy. A theoretical model describing the evolution and replication of roughness from layer to layer throughout the structure, which is in agreement with all experimental data, is presented. We find that practically all roughness caused by the growth of the multilayer structure occurs at spatial frequencies which are too high to produce scattering. The substrate roughness is replicated at lower spatial frequencies which might produce scattering within the field of view of an instrument. However, roughness in this range is below the 0.5 A level, again resulting in insignificant amounts of scatter.

Spiller, Eberhard↗