The term image quality can, unfortunately, apply to anything from a public relations firm's discussion to a comparison between corner drugstores' film processing. If we narrow the discussion to optical systems, we clarify the problem somewhat, but only slightly. We are still faced with a multitude of image quality measures all different, and all couched in different terminology. Optical designers speak of MTF values, digital processors talk about summations of before and after image differences, pattern recognition engineers allude to correlation values, and radar imagers use side-lobe response values measured in decibels. Further complexity is introduced by terms such as information content, bandwidth, Strehl ratios, and, of course, limiting resolution. The problem is to compare these different yardsticks and try to establish some concrete ideas about evaluation of a final image. We need to establish the image attributes which are the most important to perception of the image in question and then begin to apply the different system parameters to those attributes.

Based on a wide variety of fragmentary evidence taken from psycho-physics, neurophysiology and electron microscopy, it has been possible to put together a very widely applicable conceptual model of photopic visual threshold performance. Such a model is so complex that a single comprehensive mathematical version is excessively cumbersome. It is, however, possible to set up a suite of related mathematical models, each of limited application but strictly known envelope of usage. Such models may be used for assessment of a variety of facets of visual performance when using display imagery, including effects and interactions of image quality, random and discrete display noise, viewing distance, image motion, etc., both for foveal interrogation tasks and for visual search tasks. The specific model may be selected from the suite according to the assessment task in hand. The paper discusses in some depth the major facets of preperceptual visual processing and their interaction with instrumental image quality and noise. It then highlights the statistical nature of visual performance before going on to consider a number of specific mathematical models of partial visual function. Where appropriate, these are compared with widely popular empirical models of visual function.

Two hundred fifty transparencies, displaying a new digital database consisting of 25 degraded versions (5 blur levels x 5 noise levels) of each of 10 digitized, first-generation positive transparencies, were used in two experiments involving 15 trained military photointer-preters. Each image is 86 mm square and represents 40962 8-bit pixels. In the "interpretation" experiment, each photointerpreter (judge) spent approximately two days extracting essential elements of information (EEls) from one degraded version of each scene at a constant Gaussian blur level (FWHM = 40, 84, or 322 Am). In the scaling experiment, each judge assigned a numerical value to each of the 250 images, according to its perceived position on a 10-point NATO-standardized scale (0 = useless through 9 = nearly perfect), to the nearest 0.1 unit. Eighty-eight of the 100 possible values were used by the judges, indicating that 62 categories, based on the Shannon-Wiener measure of information, are needed to scale these hardcopy images. The overall correlation between the scaling and interpretation results was 0.9. Though the main effect of blur was not statistically significant in the interpretation experiment, that of noise was significant, and all main factors (blur, noise, scene, order of battle) and most interactions were statistically significant in the scaling experiment.

Research has been conducted in Perkin-Elmer's laboratories over a several-year period in an attempt to assess existing summary measures of image quality and to evolve new measures. A properly validated image quality measure would allow prediction of quality from an information content view-point that may be used in the synthesis, design, or evaluation of electro-optical sampled image systems. To further this goal, a set of psychovisual ranking experiments are presented and described in this paper. These experiments are intended to determine the influence of the sampling process, optical transfer function (OTF) shape, and OTF anisotropy on subjective image quality of sampled image systems. A description is given of the methods of experimentation employed, the procedure for providing a series of sensitometrically calibrated standards and test images for rank-ordering experiments, and the results of the tests that were performed. In addition, this paper summarizes an analysis of experimenter rankings to determine the degree of agreement (coefficient of concordance) among observers.

The 19th century art of shadow imaging, as started by Wedgwood (1803), and as used by William Henry Fox-Talbot (1851) in England, has been revived by using a small-area electronic flash lamp and fine grain film. One immediate application has been the photographic recording of large samples of living plankton. The purpose of this paper is to re-examine the resolution of the shadow system, and to describe some of the strobe light sources that are presently available. Also, a modified method of shadow photography is described where enhanced color images give interesting and, perhaps, important color effects that may be useful in the study of plankton and other semitrans-parent subjects.

The performance of image intensifiers is rated according to their capability of detecting, recognizing, and identifying objects at low light levels. The most important characteristics limiting these capabilities are noise and imaging parameters. Noise parameters are normally expressed in signal-to-noise ratios, whereas imaging parameters are described by the modulation transfer function and veiling glare. This paper will describe the methods used at the Night Vision Laboratory to determine these parameters and report typical results.

The concept of optical image quality is extended to include the total electro-optical system performance. A complex software package called the End-to-End simulation has been developed with the total system performance as its merit function. The example discussed has as its merit function, time delay errors. Subsystems modeled include the object, the "real" optical system, the detector and its associated circuitry, and the electronics used in signal processing. Validation of the modules comprising the total package is discussed.

Concepts, measures, and models of image quality are shown to be quite important in pattern recognition applications. Pattern recognition of imagery subjected to geometrical differences (such as scale and rotational changes) and intensity differences (such as arise in multispectral imagery) are considered. After modeling these image differences as a stochastic process, the optimal filter is derived. This filter is shown to be the principal component of the data. This pattern recognition algorithm is verified using multi-sensor imagery, and the results are found to compare favorably to those obtained using other candidate techniques.

Characteristics of radar scattering, the synthetic aperture radar (SAR) imaging process, and display devices are considered with respect to their effects on the quality of the resulting image. A set of SAR image quality measures which relate to application information requirements are specified, and associated measurement techniques are presented.

Angle of Incidence Reflectance Spectroscopy (AIRS) of specular surfaces of condensed materials (solids and liquids) provides detailed information on the materials' intrinsic properties. By measuring the reflectance at one or more large angles of incidence for radiation, polarized either parallel (Rp) or perpendicular (Rs) to the plane of incidence, one gets the information necessary to solve the Fresnel relationships for the components of the complex dielectric function at the incident radiation wavelength. Experimental difficulties with absolute reflectance measurements make it desirable to measure the ratios RP /RP at a minimum of two angles of incidence. An algorithm for AIRS has been devised for use with optically isotropic materials, which requires Rp/Rs values for two angles of incidence (preferably which include the pseudo-Brewster angle OB). When a thin (d1 /A <0.05) transparent layer coats the substrate, one can solve directly for two of the four parameters (substrate indices n, k; layer index n1; and layer thickness di) given the other two. An example is given for an InGaAsP specimen where k is known, or can be reasonably estimated, as well as the value of n1. Alternatively, when n1 and d1 are known, the substrate indices can be established. The experimental apparatus is essentially the same as that for pseudo-Brewster angle mea-surements. However, because AIRS does not require the direct determination of 'PB and the ratio at that angle, the gathering of spectral data is greatly simplified.

In this paper a modified analysis method for analyzing time-average defocused speckle photographs is presented. Resolved surface slope components along the examining line can be found by measuring fringe distances from a certain point. Then amplitude changes and bending moments can be calculated. The method has been verified experimentally by examining vibrations of a rectangular glass fiber multilayer plate.

The image quality of a high resolution x-ray telescope is determined both by the accuracy to which the optics can be figured and by the smoothness of the reflecting surfaces. The former determines the angular resolution, and the latter, through scattering, affects the fraction of flux within the resolution element. This paper describes a research program designed to enhance the understanding and characterization of x-ray reflecting surfaces with regard to their scattering properties. Included are representative measurements, at the subarcsecond level, of the x-ray scattering from a variety of flat reflectors, and measurements of the surface roughness of a large number of flat reflectors by more traditional methods. This work is part of a technology study for the Advanced X-ray Astrophysics Facility, a near earth-orbiting x-ray observatory to be launched by the Space Shuttle in the late 1980's

In light beam deflection technique achieved by mechanical means, the line image produced, as the polygon rotates, is not straight. A compromise between curvature, working f/number, radius of curvature, and angular deflection has been found.

This paper analyzes the device characteristics of acousto-optic Bragg cells for signal processing applications. Design parameters of efficiency, bandwidth, resolution and side lobes, and distortion are considered. Phase distortion is of particular importance in imaging type acousto-optic signal processors such as correlators and convolvers. Techniques for optimizing these performance fac-tors are discussed.

This paper will describe the design of two infrared optical pyrometers used to study dust explosions. One is a six-wavelength pyrometer which can measure both dust particle temperature and gas temperature by observing continuum and gas band emission in the 1 to 5µm infrared region using PbSe detectors. The second pyrometer measures particle continuum emission in the 0.8 to 1.0 µm region of the near infrared using Si detectors. Temperature data are presented for both laboratory and full-scale mine explosions.

Abstract. Images of objects and scenes on earth taken from high and low altitude aircraft have been used for many purposes, including natural resource analysis, weather prediction, and navigational aid. For an image of low contrast, the amplitude variations of the high frequency components of the video are small and can be masked by noise introduced during recording and transmission. Digital and analog image processing techniques are used to enhance and retain the detail information of the scene represented by the high frequency components. Experimental results are presented for the processing of optical and radar images.

Several aspects of the direct modulation characteristics of semiconductor lasers are discussed, including a brief review of some basic theory and a description of a computer-controlled measurement technique. Methods of extending the modulation bandwidth by changing external and internal parameters are also discussed. Proton-isolated tilted-facet and Zn-diffused window and continuous-stripe lasers are used as examples of devices which allow the modulation bandwidth to be controlled by varying parameters such as the photon lifetime, the spontaneous emission factor, and other aspects of the cavity 0. Measurements demonstrating modulation bandwidths of 6 to 7 GHz are also presented.

This article discusses various methods for steering the line-of-sight of an optical system based on controlling a subsystem or a single optical element. The applicability of some of the methods for line-of-sight stabilization is discussed.

Inverse-square sensitometry for low kVp techniques is limited by air attenuation and beam hardening. It is thus difficult to obtain accurate H and D curves for mammographic screen-film combinations at technique factors used clinically. Methods are described for the determination of characteristic curves at low x-ray energies which provide composite intensity-scale curves using small changes in source-to-receptor distance and concomitant changes in either exposure time, beam attenuation, or kVp. H and D curves obtained at low kVp's using the various sensitometric approaches are compared with those obtained using inverse-square sensitometry; the relative merits of the different methods are discussed.

In this paper, we develop an image enhancement algorithm that modifies the local luminance mean of an image and controls the local contrast as a function of the local luminance mean of the image. The algorithm first separates an image into its lows (low-pass filtered form) and highs (high-pass filtered form) components. The lows component then controls the amplitude of the highs component to increase the local contrast. The lows component is then subjected to a nonlinearity to modify the local luminance mean of the image and is combined with the processed highs component. The performance of this algorithm when applied to enhance typical undegraded images, images with large shaded areas, and also images degraded by cloud cover will be illustrated by way of examples.

A simple optical scanner has been designed to inspect bearing balls for surface defects. The scanner employs a fixed semicircular array of light sources to illuminate a rotating ball and an adjacent fixed array of light detectors to detect deviations from specularity on the ball surface. Each detector signal is processed by a separate channel of threshold detection electronics. The ball scanner must be able to inspect (track) balls which translate slightly as they rotate. To achieve high sensitivity and uniform surface coverage, a permanently balanced array of directional sources was built using fiber optics. Individual sources which can be accurately positioned and pointed were constructed using plastic fiber light guides and special cone shaped output apertures. Test results indicate that this scanner can reliably detect defects as small as 0.25 mm in diameter.

Fiber optics operating in the mid-infrared (IR) offer the potential for lower losses and better tolerance to nuclear radiation than current silicate-based fibers. Moreover, mid-IR fibers may be useful for a variety of shorter distance applications such as laser surgery, spot welding, and infrared integrated optics. Although a wide array of potentially highly transmissive mid-IR materials are available in bulk form, most are not suitable for fiber fabrication. Recently, however, a variety of new multicomponent glasses based on the fluorides of heavy metals have been developed, which may offer the best prospects to date for high performance mid-IR fibers. A critical comparison of the advantages as well as the problems associated with various prospective materials and fiber fabrication techniques is given.

Recently, a set of conditions has been developed under which a sequence is uniquely specified by the phase or samples of the phase of its Fourier transform. These conditions are distinctly different from the minimum or maximum phase requirement and are applicable to both one-dimensional and multi-dimensional sequences. Under the specified conditions, several numerical algorithms have been developed to reconstruct a sequence from its phase. In this paper, we review the recent theoretical results pertaining to the phase-only reconstruction problem, and we discuss in detail two iterative numerical algorithms for performing the reconstrucction.

This paper describes measurements of pollutants and water vapor in the troposphere using the differential absorption lidar (DIAL) technique. Emphasis is placed on research that has been conducted at the NASA Langley Research Center (LaRC) with ground-based and airborne lidar systems. Measurements of sulfur dioxide in power plant plumes have been made with a mobile DIAL system operated near 300 nm. Comparisons of sulfur dioxide concentrations determined with the DIAL system and in-stack monitors were found to be in agreement to within 18 percent. Vertical water vapor profiles with a ground-based lidar system have been measured using the water vapor absorption line at 724.3 nm. Rawinsonde and DIAL water vapor profile data were shown to agree within 10 percent to an altitude of 2.5 km. A multipurpose airborne DIAL system was recently developed at LaRC to investigate a wide range of tropo-spheric gases. The first remote measurements of ozone profiles from an air-craft were made in May 1980. Subsequently, the airborne DIAL system participated in a major field study with the Environmental Protection Agency (EPA) to investigate elevated pollution episodes. Results from these experi-ments are presented in this paper. Simulations are also discussed for airborne DIAL measurements of sulfur dioxide, water vapor, and nitrogen dioxide. An extensive study of the scientific rationale and potential experiments with a Shuttle lidar system has recently been completed by NASA. The application of a spaceborne lidar to uniquely measure tropospheric gases in the late 1 980s is addressed in this paper.

Holographic optical elements (HOEs) recorded with arbitrary aspheric wavefronts can now be analyzed with a holographic ray-tracing design program. The recording wavefronts are defined by analytical phase functions, for example, a two-dimensional polynomial expansion. The coefficients of the functional representations of the HOE recording wavefronts are used as parameters to optimize the performance of an optical system containing the HOE. The optimum recording wavefronts are then produced with the help of computer-generated holograms. Several useful arbitrary wavefront phase functions are discussed. Design predictions and experimental results are presented for a holographic Fourier transform lens recorded with the aid of a computer-generated hologram.

The infrared telescope (IRT) on Spacelab 2 will be the first cryogenically cooled telescope operated from the Orbiter. The principal objectives, consistent with those of the second Spacelab mission, are to measure the induced environment about the Orbiter and to demonstrate the ability to manage a large volume of superfluid helium in space. The prime astrophysical objectives are to map extended sources of low surface brightness infrared emission, including the zodiacal light, the galactic plane, and extragalactic regions. The IRT consists of a 250 liter helium dewar and an articulated cryostat containing the telescope, which scans ±45 degrees about a single axis orthogonal to both the local vertical and the Orbiter pitch axis. The telescope is an f/4 15.2 cm highly baffled Herschelian telescope cooled to 8 K, which may scan to within 35 degrees of the sun. The focal plane cooled to 3 K consists of nine discrete photoconductors covering a wavelength interval of 4.5 to 120 microns in five bands. Each detector has a 0.6 X 1.0 degree field of view. A single 2 micron stellar detector is used for aspect determination. A cold shutter provides a zero flux reference. Overlapping scans, contiguous orbits, and a six degree per second scan rate permit rapid redundant coverage of 60% of the sky.

The burning of grasses, other cellulosic vegetation materials, motor vehicles and their organic polymeric constituents, and common petroleum liquid fuels yield fire-generated products such as smoke particulates (usually a complex mixture of solid and/or liquid organic materials or substances predominantly carbonaceous or soot-like in character) and heat. The fire products have been identified and the factors which govern their concentrations are presented. The incentive for this study derives from the need to evaluate the performance of electro-optical sensors in adverse environments.

By long tradition and for sound reasons, certain topics are considered inappropriate as subjects for editorials and other matter in scholarly journals. I now propose to discuss one of those topics. The topic is money. In particular, the topic is publication charges and how Optical Engineering deals with them.