Aperture Correction Research Articles

Underwater Imaging System Techniques

The present performance capability of underwater low-light-level television (LLLTV) cameras used in biological and geological survey applications is discussed. Video-processing techniques are shown to be useful to improve contrast loss due to backscatter, to provide vertical aperture correction and to reduce systematic shading patterns. Performance of present underwater television systems can be improved by using such techniques.

ON APERTURE CORRECTIONS FOR COMET MAGNITUDE ESTIMATES

ABSTRACT The results of a study into the effects of aperture on the observed brightness of comets are presented. Observations of 22 comets were used to determine the average aperture corrections for refractors and reflectors. The resulting aperture correction for refractors was only slightly less than that found by Bobrovnikoff. However, the aperture correction for reflectors was found to be less than one-third the value found by Bobrovnikoff for refractors. Key words: comets - magnitude estimate

The Redshift-Distance Relation. I. Angular Diameter of First Ranked Cluster Galaxies as a Function of Redshift: the Aperture Correction to Magnitudes

view Abstract Citations (227) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Redshift-Distance Relation. I. Angular Diameter of First Ranked Cluster Galaxies as a Function of Redshift: the Aperture Correction to Magnitudes Sandage, Allan Abstract Micrometric estimates of the apparent angular diameters of first-ranked elliptical galaxies in clusters, obtained from a homogeneous series of plates taken with the Palomar 48-inch (122 cm) Schmidt and the Hale reflector, are tightly correlated with redshift, such that 0 z '. The cosmic dispersion about the mean correlation is a(A log 0) 0.07, which is close to `5 (AV), where AV is the deviation of apparent magnitude of these same galaxies from the Rubble diagram. This relation suggests constant mean surface brightness for first-ranked ellipticals, as does correlation of the individual magnitude and diameter residuals. The theoretical 0 = J(z, qo) relations derived for Friedmann models shows that qo may eventually be found from accurate microphotometry of such plates (or direct photoelectric area scanning). The predicted differences in the diameter function for various qo values are adequately large compared with the intrinsic dispersion (T(A log 0) for test galaxies at z > 0.4 to make such a program feasible. The growth curve of magnitude with measuring aperture is obtained from new photoelectric data listed in Papers II and III. The aperture correction follows from this formulation as a function of z and qo alone for first-ranked ellipticals. A method for differential correction of the aperture function is developed that takes account of cosmic differences in intrinsic diameters and different qo values Publication: The Astrophysical Journal Pub Date: May 1972 DOI: 10.1086/151440 Bibcode: 1972ApJ...173..485S full text sources ADS | data products NED (76) Related Materials (9) Part 2: 1972ApJ...178....1S Part 3: 1972ApJ...178...25S Part 4: 1973ApJ...180..687S Part 5: 1973ApJ...183..711S Part 6: 1973ApJ...183..731S Part 7: 1973ApJ...183..743S Part 8: 1975ApJ...202..563S Part 9: 1986ApJ...307....1S Part 10: 1987ApJ...317..557S

Electronic techniques for radiological image processing.

A television image processing system for diagnostic radiology using the techniques of contrast enhancement, aperture correction, and highlight inversion is described together with a method for objectively evaluating its usefulness. The evaluation is done by comparing error rates of observers viewing a specially prepared set of chest radiographs through the image processor with error rates using a conventional viewbox. The error rates of different processing techniques are given and conclusions about the causes of these error rates are drawn. These conclusions, in turn, yield guides for the future design of circuits to improve the performance of image processors.

Advanced Techniques for Plumbicon Cameras

Research has improved the picture quality in Plumbicon cameras since their introduction. Pictures with higher definition have been obtained with newly developed focus and deflection coil-assemblies and by operation at an increased anode voltage. Methods to increase apparent sharpness include advanced aperture correction and application of anti-halo glass buttons. Techniques to improve color rendition are discussed.

New CBC Vidicon-Telecine Operating Standards: With Particular Reference to the Gray-Scale Characteristic

The results presented are from an investigation to obtain optimum picture quality in 16mm vidicon-telecine installations of the Canadian Broadcasting Corp. Picture quality is examined in terms of signal-to-noise ratio, resolution, gray-scale rendition and lag. As a consequence to the investigation, new standard values of the vidicon peak-white signal current, aperture correction and gray-scale correction are about to be introduced into CBC operations. — The telecine gray-scale characteristic is plotted together with a typical 16mm print-through characteristic. The resultant curve is shown to be similar to that of the image-orthicon camera. The measurement of the gray-scale characteristic, using the Holmes-CBC slide, is shown to be distorted by shading errors, and a new slide is introduced to minimize this problem.

Instrumental Corrections in Measurements of Gas Dispersion A Three-Slit Problem*

Instrumental corrections have been worked out for a gas refractometer of the hollow prism type used in conjunction with a monochromator. Three slits are involved: entrance slit of the monochromator; exit slit of the monochromator, which is also the entrance slit of the refractometer; and exit slit of the refractometer. The treatment constitutes an extension of the familiar slit and aperture correction procedures that have been worked out for a monochromator alone. The specific objective is the accurate determination of the absolute strengths and widths of individual lines in the refraction spectrum of gases. An example is given of this application.

Fluctuation noise in television-camera head amplifiers

The usual input circuit for a head amplifier associated with a pick-up tube of the C.P.S. Emitron type is effectively a capacitance shunted by a resistance, the former consisting of the output capacitance of the tube and the input capacitance of the amplifier. An improvement in signal/noise ratio for the higher video frequencies is shown to be obtainable by modifying the input circuit by connecting an inductance between the two capacitances, and suitably equalizing the modified frequency/amplitude response. A weighting function is suggested for assessing the visual effect of the two differing noise spectra. The increase in noise resulting from the application of aperture correction for the pick-up tube response is considered, and some of the noise problems associated with gamma correction are discussed.The latter half of the paper describes a method of equalizing the frequency/amplitude response of the modified input circuit and considers some of the practical problems involved in designing a low-noise head amplifier. The conclusion is reached that a worthwhile improvement in picture quality is obtained by modifying the input circuit, and this is particularly so when aperture correction is used.