Showing papers on "Image quality published in 1976"

Image retrieval from astronomical speckle patterns

Abstract: A technique has recently been proposed for processing astronomical photographs to remove the effects of turbulence. The method involves averaging over many short-exposure photographs of an object to reconstruct a diffraction-limited image of the object. A two-dimensional computer simulation of the reconstruction technique is presented. The results indicate that diffraction-limited imaging with a 100 in. telescope is possible even with 2 arc sec seeing conditions.

Fundamental Limitations In Linear Invariant Restoration Of Atmospherically Degraded Images

Abstract: Restoration of atmospherically degraded images is limited most fundamentally by the photon noise inherent in any detected image. After presenting a general model for photon-limited images, we derive the form of the linear, space invariant filter which restores the image with minimum mean-squared error. Measures of the restorable bandwidth and image quality are developed. The theory is applied to the case of images degraded by atmospheric turbulence, both with and without perfect tilt removal. The relationship between the number of detected photoevents and the restorability of the degraded images is quantified.© (1976) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The aliasing problem in computer-synthesized shaded images.

Abstract: : This paper describes work toward improving the quality of computer-synthesized shaded images. Current (practical) hidden-surface algorithms produce an image whose precision is strictly limited by the number of picture elements. Problems caused by this limitation are described and explained in the text. Other image production media such as television and screen printing processes exhibit the same problems, but to a far lesser extent. Therefore, current image production media are surveyed and compared to computer-synthesized images with a view toward establishing a criterion for acceptable image quality. The problems to be seen in computer-synthesized images are predominantly caused by a phenomenon known as aliasing. Aliasing is an artifact of the process of producing an image made of discrete dots. A well known cure for aliasing is motivated and explained in the text. The notions of sampling and convolutional filtering are introduced to assist the explanation. Based on these techniques, an algorithm for computing the intensity of a single dot of an image is developed. The algorithm is applied to a test pattern which serves as a worst case for the problems caused by aliasing.

Scene power spectra: the moment as an image quality merit factor

Abstract: Coherent optical power spectra of random scene imagery can become a powerful image evaluation technique when properly analyzed. A normalized low order moment of power spectra is set forth as a good image quality merit factor, which also has the advantageous property of taking out the spectrum analyzer’s aperture effect. In addition to the relevant theory, experimental results with this merit factor of power spectra are given that demonstrate a high degree of correlation with subjective quality rankings, as well as the accurate assessment of optimum focus.

Image quality prediction - An aid to the Viking lander imaging investigation on Mars

Abstract: Two Viking spacecraft scheduled to land on Mars in the summer of 1976 will return multispectral panoramas of the Martian surface with resolutions 4 orders of magnitude higher than have been previously obtained and stereo views with resolutions approaching that of the human eye. Mission constraints and uncertainties require a carefully planned imaging investigation that is supported by a computer model of camera response and surface features to aid in diagnosing camera performance, in establishing a preflight imaging strategy, and in rapidly revising this strategy if pictures returned from Mars reveal unfavorable or unanticipated conditions.

Photoelectron counting with an image intensifier tube and a self-scanned photodiode array

Abstract: A self-scanned photodiode array was fiber-optically coupled to an ITT proximity-focused image intensifier tube. It was determined that a single photoelectron event produces 34,000 charge carriers in a photodiode. This charge is only a factor of 2.8 above the rms noise level of the preamplifier used in the tests, but standard charge-sensitive techniques are at least a factor of 12 better. The image tube and photodiode array combination can be packaged in a disk 5.1 cm in diameter and 2.6 cm thick.

Image quality in mammography

Abstract: In mammography, image quality is a function of the shape, size, and x-ray absorption properties of the anatomic part to be radiographed and of the lesion to be detected; it also depends on geometric unsharpness, and the resolution, characteristic curve and noise properties of the recording system. X-ray energy spectra, modulation transfer functions, Wiener spectra, characteristic and gradient curves, and radiographs of a breast phantom and of a resected breast specimen containing microcalcifications are used in a review of some current considerations of the factors, and the complex relationship among factors, that affect image quality in mammography. Image quality and patient radiation exposure in mammography are interrelated. An approach to the problem of evaluating the trade-off between diagnostic certainty and the cost or risk of performing a breast imaging procedure is discussed.

Improved performance from pyroelectric vidicons by image-difference processing

Abstract: We describe the design and performance of a pyroelectric infrared camera system which employs chopping plus image-difference processing (IDP), an approach motivated by the desire for steady, smear-free thermal images. A standard pyroelectric vidicon is scanned at a 30-Hz frame rate and chopped at 15 Hz, generating frames having alternating scene polarity. Each frame is stored in a video disk recorder, the following frame subtracted from it, and the resultant signal displayed (after inverting the polarity of alternate frames). This technique improves the sensitivity, enhances spatial resolution, eliminates fixed-pattern noise (blemishes and other nonuniformities), minimizes the effects of lag, and reduces flicker. The subjective improvement in image quality, compared to a chopped system without IDP, is considerable. Examples of imagery are included, and preliminary results of some system performance measurements are reported, indicating a minimum resolvable temperature of 1 °C at about 250 TV lines per pic...

A Large Field Image Intensifier Tube for Scintillation Cameras

Abstract: The image intensifier tube opens a new era in scintigraphic diagnosis. The first results are very promising. Because of the image quality, tumors can be detected earlier than with other systems, and more details can be perceived. In the future the quality of the image can be further improved. (auth)

Pseudo Fan Beam Reconstruction Algorithms and Their Related Physical Problems

Abstract: The pseudo fan beam reconstruction algorithm and related physical problems are considered. Image distortion related to the rearrangement to a parallel beam from a fan beam scan is discussed together with physical problems such as Compton scattering in tissue which affects the final image quality.

Survey And Analysis Of Image Coding Techniques

Abstract: A state-of-the-art survey of digital image coding techniques is presented. Performance analyses are given for pulse code modulation, statistical, frame replenishment, predictive, interpolative, and transform coding methods.© (1976) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Image Quality, a Comparison of Photographic and Television Systems

Abstract: (1976). Image Quality, a Comparison of Photographic and Television Systems. Optica Acta: International Journal of Optics: Vol. 23, No. 10, pp. 842-842.

Aberrations of spherocylindrical spectacle lenses.

Abstract: A procedure has been developed for tracing a bundle of rays through and ophthalmic lens and a schematic eye with its primary line of sight pointed through various parts of the lens. A bundle of eight rays can provide data for assessing the quality of the image formed by such a system. To test the procedure and to generate data which can help in selecting a method for evaluating image quality, we selected a single lens as an example. The lens selected has a spherical back surface (-5.00 diopters) and a toric front surface (+15.00 diopters in the vertical and /10.00 diopters in the horizontal). It has a center thickness of 5 mm and glass of index 1.523. Spot diagrams were generated with the eye pointed in various directions through the ophthalmic lens. The data generated showed that peripheral bundles which fall between the principal meridians emerge as astigmatic bundles. This leads to the proposal that blur circle theory can be used for evaluating the quality of the optical image and that it suffices in the case of a spherocylindrical ophthalmic lens to base the tolerances for refractive power on measurements made in the principal meridians.

Phase and Doppler errors in a spaceborne synthetic aperture radar imaging the ocean surface

Abstract: Data processing in a spaceborne synthetic aperture radar (SAR) imaging the ocean surface is affected by earth rotation, orbit eccentricity, and wave motion. Without compensation these sources will cause the images to shift in range and in-track positions and also cause defocusing. Ionospheric granularities may degrade image quality. Calculations of the magnitudes of these effects are presented.

Thaumascan: Improved Image Quality and Clinical Usefulness

Abstract: During the past year of clinical evaluation, several modifications have been made to the two-dimensional, real time, high resolution ultrasound imaging system known as the Thaumascan system. These modifications were designed to improve the final image quality as well as to enhance the clinical usefulness of this imaging system in assessing various cardiac disorders.

A New Nuclear Medicine Scintillation Camera Based on Image-Intensifier Tubes

Abstract: A large-field scintillation camera for nuclear medicine application has recently been developed by Old Delft. The system is based on a large-field image-intensifier tube preceded by a scintillator mosaic. A comparison is made with present state-of-the-art scintillation cameras in terms of modulation transfer function (MTF) and sensitivity. These parameters, which determine the performance of scintillation cameras, are not independent of each other. Therefore, a comparative evaluation should be made under well-defined and identical conditions. The new scintillation camera achieves considerable improvement in image quality. In fact, the intrinsic MTF of the new camera is rather close to unity in the spatial frequency range up to 1 line pair per centimeter (lp/cm). Further improvement would require a fundamentally new approach to gamma imaging, free of the limitations of conventional collimators (e.g., coded-aperture imaging techniques).

Mammographic Image Quality And Exposure Levels Using Conventional Generators And Type M Film

Abstract: With the four technical factors of controlled motion, long target-film distance, exquisite collimation and good processing meticulously cared for, conventional generators and type M film mammography can be done with skin dose less than or comparable to other contemporary mammographic techniques with far superior image quality.

Adverse effects of stationary grids.

Abstract: By means of simple tests, the mechanisms of image impairment due to stationary grids were demonstrated. Several contributing factors were found. The fact that the grid strips are not clearly visible in the film does not indicate that image quality is not lowered by the grid. To a certain degree it demonstrates that the image quality is so low that not even the grid lines are perceptible.

Blur of the Retinal Image of an Object Illuminated by Low Pressure and High Pressure Sodium Lamps

Abstract: The IES Roadway Lighting Committee sought to establish a criterion that might be used when choosing between high pressure and low pressure sodium lights. The quality of the optical image on the retina was a major consideration. The author, then serving on the IERI Technical Advisory Committee on Light and Vision, volunteered to apply to these two light sources a method that he had developed for assessing image quality in such cases. The method can also be applied to other types of light sources.

Magnifying image intensifier

Abstract: An improvement in a magnetically focused image intensifier for increasing the usable range of magnification without degradation of image quality and while keeping to a minimum the power requirements of the focusing coils. The improvement comprises an arrangement of focusing coils which reverses the direction of the axial magnetic field distribution between the planes of the photocathode and the phosphor screen.

Image Quality of Photoelectronic Imaging Systems and its Evaluation

Abstract: Publisher Summary This chapter discusses the criteria for evaluating image quality of photoelectronic imaging systems. An imaging system is used to form an image that can be interpreted by the eye in terms of the scene viewed, and which contains visual information that is not available to the eye without the device. Except for the purely optical systems, which form aerial images, imaging systems form their images on a surface, usually plane. The basic problem in evaluating image quality is to determine and quantitatively evaluate the ways in which the visual information content in the image varies from that in the scene. A complete description of the image quality of an imaging system requires evaluation at the points distributed over the volume in image space extending over the entire area of the image plane, and between the extreme positions of the image plane for all wavelengths for which the system can be used, and over the illumination range for which the system is suited. In this chapter, concepts related to the point spread function are discussed. Details of the line spread function, the edge gradient and acutance are also provided. It also elaborates the basics of optical transfer function, contrast transfer function, and limiting.

On the Use of a Television System in Image Reproduction: Part II-The Reduction of Line-Raster Effects

Abstract: This paper describes the improvement of image quality effected in a reproduction television system by reducing the visibility of the line raster. The methods of reducing the visibility of the line raster are discussed and the organization of the designed line-raster processing unit is shown. Also an image processed by the line-raster processing unit and a reference image are shown.

Fast automatic lens testing for extended-field image quality.

Abstract: Monitoring of high-volume lens manufacture for Polaroid Land photography requires an acceptance criterion that is both relevant to picture quality and suitable for automatic testing. In a hardware test based upon the modulation transfer function (MTF), the problem is to choose what not to measure, while obtaining enough information about a lens to assign it a useful figure of merit. The predominant defects of manufacture are field tilt, resulting from tilting or decentering of components, and field curvature, from small errors in spacing, thickness, radius, or index. Field tilt and curvature are not local defects of the image surface, insofar as they may be removed by a local refocus. We therefore need a test procedure that can (perhaps simultaneously) examine image quality over an extended field, but is principally called upon to evaluate focus differences. At multiple field locations a single-frequency modulation measurement adequately defines the MTF for the low spatial frequencies of interest and can be interpreted easily in terms of the rms blur of the point spread function. We will discuss the logic of 100% lens acceptance testing and two types of instrumentation we have used.

An Evaluation Of Low Light Level Television For Breast Cancer Detection

Abstract: A low light level electronic imaging system is being developed to be used in a mass screening program for breast cancer detection in asymptomatic women. In this technique a mammographic image formed from an x-ray beam collimated by a scanning slit is converted to an intensified visible image which is viewed by a high resolution isocon television camera. The signal which is displayed on a small flat-faced cathode ray tube is photographed onto 70 mm roll film. Some advantages of the system for mass screening are its low cost of operation, ability to eliminate detection of scattered x-rays, short examination time, small format film images, low radiation exposure to the breast and the capability of electronic image processing. The limiting resolution of the system has been measured using lead test patterns and a phantom containing small diameter wires. In these experiments the electronic technique clearly demonstrated a 50u wire and barely detected a 25u wire. Extensive studies of the imaging properties of the system indicate that the image quality is limited chiefly by the television noise. In a clinical study, the ratio of the radiation exposure for the electronic method compared to that for the Lo-Dose film screen technique was measured at 0.17 + 0.06. At this level of exposure, the quality of the images was adequate to demonstrate cancers, calciTications, tumors, skin thickening, and trabecular structure. Calcification can be demonstrated, but at this Stage of development, very fine calcifications are not adequately visualized.

Image processing by nutation: an analysis.

Abstract: Enhancement of blurred images by nutation involves accumulation of information from displaced replicas of the degraded image. The technique is analyzed theoretically and is found to be equivalent to convolution with the weight distribution assigned to the replicas. The process is shown to improve resolution, correct certain aberrations, or reduce effects of noise, when adjustable parameters are properly selected. Plots of spectrum enhancement and of SNR calculations are presented, and tradeoffs between resolution and noise are discussed.

Geometric assessment of image quality using digital image registration techniques

Abstract: Image registration techniques were developed to perform a geometric quality assessment of multispectral and multitemporal image pairs. Based upon LANDSAT tapes, accuracies to a small fraction of a pixel were demonstrated. Because it is insensitive to the choice of registration areas, the technique is well suited to performance in an automatic system. It may be implemented at megapixel-per-second rates using a commercial minicomputer in combination with a special purpose digital preprocessor.