Showing papers on "Image quality published in 1974"

Quantitative Effects of Stationary Linear Image Processing on Noise and Resolution of Structure in Radionuclide Images

Abstract: Processing radionuclide image data in an attempt to improve its diagnostic usefulness inevitably changes both the noise and the resolution of structures in the image. Although at present little conclusive evidence exists to indicate whether or not image processing is beneficial, an understanding of the quantitative effects of various processing techniques on parameters of resolution, noise magnitude, and noise texture seems to provide a useful beginning towards solution of the more difficult problem of understanding the effects of image processing on diagnostic image quality. Quantitative effects of stationary linear image processing procedures, which include all convolutions and filtering operations, can be predicted rather simply. In the present work, expressions for predicting these quantitative effects are developed and are applied to computer-synthesized image data to provide illustrative examples of the effects of typical noise-smoothing and resolutionenhancing operations. (auth)

Calculation of Axial Polychromatic Optical Transfer Function

Abstract: Polychromatic or white-light OTF is put forward as a criterion of image quality for systems under actual working conditions. The formulae necessary to extend from the monochromatic to the polychromatic OTF are developed for the axial case. A computer programme has been developed and calculated results are compared with measurements.

An Approach to Image Quality Evaluation, Using Observer Performance Studies

Abstract: The most difficult problem in radiologic image research is the derivation of a function describing the quality of the radiologic image in terms of physical factors of the imaging process. It is suggested that observer studies can aid in the solution of this problem. To this end it is necessary to design studies which separate the variables affecting detail visibility and to use an idealized test object containing only resolution and noise-limited detail in order to reduce the complexity of the experiments. A broad outline for such studies is presented.

Adaptive imaging telescope with nonlinear quadrant sensing and electro-optical phase shifting

Abstract: An adaptive imaging telescope having nonlinear sensing means for detecting an optical image received thereby. The system comprises a phase shifter, positioned at the aperture of the telescope or at an image plane thereof. This system also includes a nonlinear image quality sensor optically coupled to the phase shifter, consisting of a quadrant nonlinear detector wherein each detector element of the quadrant detector is responsive to light from the optical image, the quadrant detector comprising nonlinear photocells or detectors whose plane is positioned at an image plane of the telescope. The photocells are connected to a network for providing image quality error signals. Analog circuits are provided to receive the sensor output and provide a closed-loop return to the phase shifter.

Evaluation Of Noisy Images

Abstract: The quality of an image is evaluated by an observer by a subjective comparison with image impressions stored and remembered more or less distinctly. A photographic print for example, is judged by its gray-scale, sharpness or definition; and its graininess. The subjective ranking of "poor, good or excellent" depends on the size of the print and the viewing distance, and may change substantially when an excellent print is available for a direct comparison. A study of images on an objective basis has but one purpose: to determine objective criteria which will correlate with visual observations. It is evident that the characteristics of the visual system must be included in an objective evaluation of image quality.

Coded Aperture Gamma-Ray Imaging With Stochastic Apertures

Abstract: A number of schemes employing coded apertures are currently under investigation for in vivo imaging of gamma-emitting tracers. These schemes are based on stationary aperture codes, which depend upon having a cleanly peaked spatial auto-correlation function to facilitate faithful recovery of the source distribution. The image is recovered by performing a spatial integration optically, digitally, or by some other suitable means. This paper describes an alternate method based on time modulated apertures with digital image reconstruction. In contrast to the stationary aperture, the time modulated aperture requires no spatial integration to achieve faithful reproduction of the source distribution. This solves the problem of false structure arising from out-of-focus sources. Good 3-dimensional point response functions free of side lobes have been obtained and it is expected that this approach will yield high quality clinical images.

Evaluation of Digitally Corrected Erts Images

Abstract: The discussion is limited to processes by which a set of data samples collected on a geometrically distorted grid can be converted to samples on a different precisely specified grid It is assumed that a mathematical expression for the desired transformation already exists Concern will be the effects on image quality (specifically loss of resolution, photometric accuracy, and miscellaneous aberations) that result from various techniques used in accomplishing the resampling The resampling techniques evaluated have included nearest neighbor, bilinear, cubic convolution, and various truncated versions of sinc (x) The conclusion is that cubic convolution yields substantially higher quality output data for scenes typically encountered and can, in some instances, substantially enhance one's ability to abstract information

Real‐time synchronously pulsed ir image up‐conversion

Abstract: Real‐time ir image up‐conversion has been achieved using a synchronously pulsed mode of operation for both the pump and ir sources. Operating at 133 pulses/sec, the up‐converted images were readily viewed on an ordinary S‐1 surface image intensifier tube. Optimization and adjustments of image quality were accomplished easily in real time.

Adaptive imaging telescope with camera-computer transform image quality sensing and electro-optic phase shifting

Abstract: An adaptive imaging telescope having a linear sensor for detecting a received optical image. The system includes a choice of two electro-optic phase shifters positioned substantially at the aperture of the telescope responsive to the received optical image. A non-coherent image quality sensor is provided consisting of a video camera and digital computation networks. This system also includes circuits responsive to outputs from the sensor feeding the phase shifter in a closed-loop arrangement.

Subjective Assessment And Specification Of Color Image Quality

Abstract: A practical image quality criterion was developed which is easily calculated anddirectly measurable and which gives consis-tent evaluations of system performance. Theimage quality merit function was evaluatedfor a wide variety of MTF shapes which includechromatic and nonsymmetric image errors. Theresults of the experimental program are thatthe image quality merit function is able topredict image quality within normal readererror and is linearly correlated with themeasured data. The tests of the proposed quality criterion for color and black -and-white images have been limited to physicallyrealizable optical systems producing grain -free images and to a range of image qualityfrom excellent to unusable.INTRODUCTION When an optical system has been designed andbuilt, the optical engineer is faced with answering the following question: "Does thisoptical system meet the intended imaging taskrequirements ?" One way of ascertaining this is by having a panel rate the system's per-formance by judging a variety of images.These subjective assessments are often oflimited accuracy and offer the system's de-signer little information other than that hissystem passed or failed the panel's imagequality criteria.Ever since the introduction of the OpticalTransfer Function (OTF), efforts have beenmade with varying success to provide an analy-tical bridge between the OTF and a subjectivemeasurement of image quality. The problemremains that the OTF, which is recognized asthe most inclusive measure of system perfor-

The OTF In Electro-Optical Imaging Systems

Abstract: The subject of image assessment and specification is of canonical importance to those involved in the research, development, and utilization of imaging systems. The quantitative assessment of something as subjective as the value of an image is essential in quantifying and communicating the needs and results of an imaging system or its components. In spite of the urgent need and the vigorous effort of the technologist responding to this need, no universally accepted standards for the measurement of image quality are available. The utilization of Fourier methods in image assessment and specification problems is currently in vogue because of their dexterity in fulfilling at least two necessary conditions as a measure of image quality. First, the Fourier methods provide a quantitative measure of image quality which reasonably correlates with the subjective effectiveness of an imaging system, and second, the analysis and performance prediction of a cascaded imaging system from a knowledge of the performance of its individual components are facilitated.© (1974) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Sensor performance evaluation of the Skylab multispectral photographic facility

Abstract: Results of resolution tests for multispectral imagery from Skylabs 2, 3, and 4 are presented. Methods employed were visual edge matching and edge slope analysis, and resolution was evaluated as a function of spectral band, EREP pass, target orientation, field of view, exposure, and contrast. Preflight and postflight image quality data were compared. The multispectral image quality has equaled or slightly exceeded design predictions.

The Effects of Circuit Parameters on Image Quality in a Holographic Acoustic Imaging System

Abstract: The design of holographic acoustic imaging systems using hydrophone arrays at the Naval Undersea Center has led to the development of special signal processing electronics which will be described in detail. The tolerances on electronic component values in this circuit, the major noise sources in the circuit, and other properties of an imaging system will be used to calculate the expected imaging performance of a holographic imaging system, as measured by its image dynamic range. An alternative version of the circuit will also be discussed, analyzed, and compared with the original circuit. Finally, an analogy between the signal processing circuit and a cross-correlator will be made, indicating possible future developments.

Rapid Evaluation Of Extended-Field Photographic Quality Of Lenses

Abstract: Monitoring of high-volume lens manufacture for Polaroid Land photog-raphy requires an acceptance criterion which is relevant to picture quality and suitable for automatic testing. In a hardware test based upon the Modu-lation Transfer Function, 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 the 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 which can (perhaps simultaneously) examine image quality over an extended field, but which 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 root-mean-square blur of the Point Spread Function. We will discuss the logic of 100% lens acceptance testing and two types of instrumentation we have used.

Testing Image Quality In Electro-Optical Devices

Abstract: Electro-optical devices present a much more complex testing problem than pure optical systems. An optical system is normally fixed and passive making it independent of light level used in testing. An electro-optical device, however, may have gain, wavelength conversion, and electronic or mechanical dynamics associated with their mode of operation. In addition, these systems may use direct imaging, array scanning or line scanning techniques in their image display system. Image testing, therefore, may have to be performed at low light levels in high gain systems to prevent damage to the photocathode. The device may have to be gated in synchronism with the display. For systems with automatic brightness control, the operating point of the imaging test must be carefully defined in order to get accurate and repeatable data. All of these factors must be considered to get valid data on the image quality of electro-optical devices. This paper will cover the generic system types and typical testing configurations for performing these measurements.

SAR image quality analysis model

Abstract: : The report describes a SAR (Synthetic Aperture Radar) image quality analysis and an image quality model incorporating the conclusions of the image quality analysis into a SAR system digital simulation. The objective of the model and its development program is to provide a fundamental approach for SAR image quality effects for specific SAR systems (parameter combinations performing specific missions). The model thus provides a relatively economical prediction of the information which can be extracted from a specified radar- mission configuration. The model output is a collection of image quality assessment functions, in particular the TQF (Threshold Quality Factor). Other parameters, which indicate the performance of the SAR system, are available from the digital simulation. These include the point target response (both range and azimuth) along with their locations for a preselected target field configuration.

Application of an electronic image analyzer to dimensional measurements from neutron radiographs

Abstract: Means of obtaining improved dimensional measurements from neutron radiographs of nuclear fuel elements are discussed. The use of video-electronic image analysis relative to edge definition in radiographic images is discussed. Based on this study, an edge definition criterion is proposed for overcoming image unsharpness effects in taking accurate diametral measurements from radiographs. An electronic density slicing method for automatic edge definition is described. Results of measurements made with video micrometry are compared with scanning microdensitometer and micrometric physical measurements. An image quality indicator for estimating photographic and geometric unsharpness is described. (auth)

Cross-spectrum error criterion as an image quality measure.

Abstract: Various criteria have been considered for image quality measure. Some of these involve subjective human visual evaluation, while others rely on statistical techniques. In this paper, a cross-spectrum error criterion is considered as a distortion measure for undersampled band-limited images. The effect of undersampling, aliasing on the perfect image, is demonstrated by manipulation in the frequency domain. Subjective comparison of the digital simulation results and the appropriate calculated spectral error indicate that the latter is a useful quantity for the analysis of distortion present in undersampled images. Relevance of our analysis to spatial filtering experiments and the mean square error is also discussed.

A Survey Of Numerical Techniques In Image Evaluation

Abstract: This survey of image evaluation by numerical techniques makes no pre-tense of surveying the entire field of image evaluation. It has been directed to some of the subjects considered to be particularly timely and of broad interest. The numerical techniques involved in the solution of various problems in image evaluation or image analysis will be covered.© (1974) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Tilted Component Optical Design Methods For The Infrared

Abstract: The eccentric pupil ("off axis") paraboloid is the most pop, ar optical system for the infrared because there are no obstructions in the light path. However, the field of view is limited owing to coma. Better overall image quality can sometimes be obtained by using a spherical mirror such as found in the quasi-Schmidt systems. Image quality not withstanding, we often find that we need a long focal length in a short space, and so we look toward more elaborate optics than a single mirror. Two-mirror reflectors, such as the Cassegrain, can be made with an eccentric pupil so that there is no obstruction, or with a Gregorian (concave secondary, intermediate image) reflector, which is commonly used in infrared telephoto systems.

Current status of diagnostic counting and imaging techniques used in nuclear medicine: A sketch

Abstract: Diagnostic procedures used in Nuclear Medicine are designed to provide information about the static and/or dynamic distribution of some particular stable or radioactive material within the patient, as well as the quantity of the material present. Thus, the static distribution of 131I in the thyroid indicates the structure of the gland, whereas changes in the distribution or in the quantity present indicate its rate of functioning. A remarkable variety of techniques, based on emission, transmission, fluorescence, and incoherent holographic imaging principles, have been developed. Both moving and fixed radiation detectors are used, and these produce planar and 3-D projections and transverse sections of the object of interest. In general, the image quality is determined by detector characteristics such as sensitivity, spatial resolution, and depth of field, as well as by the examination time, object contrast, and object intensity, which is always severely limited in the interest of a low radiation dose to the patient. Image processing techniques can be used to improve image quality by removing certain artifacts and by producing a degree of sharpening that is limited by the signal-to-noise ratio. Incoherent holography and optimum-weighted multichannel imaging are presented as two approaches to increasing the signal-to-noise ratio. Alternative criteria for the evaluation of imaging procedures are presented, with an emphasis on the use of ROC curves to describe observer performance.

An Approach to Image Quality Evaluation, Using Observer Performance Studies 1

Abstract: The most difficult problem in radiologic image research is the derivation of a function describing the quality of the radiologic image in terms of physical fac­ tors of the imaging process. It is suggested that observer studies can aid in the solution of this problem. To this end it is necessary to design studies which separate the variables affecting detail visibility and to use an idealized test object containing only resolution and noise-limited detail in order to reduce the complexity of the experiments. A broad outline for such studies is presented. BSE RVE R performance in the detection of radio­ graphic detail depends on factors related and unrelated to the quality of the radiographic image. This discussion is concerned only with those as­ pects of observer performance which are related to image quality. In this context, the evaluation of observer per­ formance can serve two major purposes: First, to intercompare the visual performance of dif­ ferent radiologists looking at the same radiograph. This is actually an evaluation of the observers' visual system alone, because differences in ex­ posing and recording conditions do not exist and therefore do not affect the result. Second, to study a radiologist's relative ability to detect detail when viewing radiographs of the same object made under different exposing and/or recording conditions. In this case, the evaluation of observer performance indirectly leads to an evaluation of the performance of the radiologic imaging process. Interobserver differences gen­ erally play only a secondary role, especially if the appearance of the radiographs, i.e., their physical image quality, differs markedly. It is this aspect of the evaluation of observer performance which is of particular interest because it is expected to aid in the solution of the most difficult problem in radiologic image research. This problem is the derivation of a number or function describing the quality of the radiologic image in terms of physical factors of the imaging process. Its solution is important not only for the evaluation of present imaging methods, but also for the efficient design and evaluation of new devices. For a meaningful approach to this problem it is OPTICAL CHARACTERISTICS