Showing papers on "Image quality published in 1968"

A test object and criteria for high resolution electron microscopy

Abstract: The desirability and requirements for a specimen capable of testing the resolving power and other image characteristics of an electron microscope are discussed in detail. In this discussion, the underlying diffraction phenomena are particularly utilized. A partially graphitized carbon black is shown to satisfy the requirements extremely well and constitutes an easily prepared specimen for conducting tests of image quality in the molecular size range. The structure of the test object is known in detail with the result that readily interpretable phase contrast images are obtained. Micrographs illustrating the use of the 3.4 A (002) spacing for magnification calibration, astigmatism and asymmetry check as well as resolving power are exhibited. The second order c-spacing of 1.7 A is occasionally found in an image. The micrographs shown herein were taken with two different electron microscopes by different operators obtaining the same structural detail in the images. It is concluded that the carbon black test object offers the best possibilities for evaluating image performance of any specimen yet suggested.

Theoretical Prediction of Image Quality

Abstract: J L Harris has indicated that a general result from statistical decision theory can be used to derive a theoretical expression for predicting resolving power We show that by appropriate choice of tasks, it is possible to obtain, from this same result, other measures which have previously been employed as image-quality criteria Our results indicate that decision theory provides a common basis for deriving quality criteria for diverse tasks Prediction of image quality for object identification is also discussed

Image quality of a gamma camera system.

Abstract: Computer calculations were made to study the image quality with respect to ` co-ordinate distortion ' of gamma camera systems of the Anger principle as a function of the design parameters: crystal dimensions, light guide length and optical properties, number, size and position of the photomultiplier tubes, and type of pulse mixing circuit. The use of ` ratio ' circuits, in which the denominator pulse and the energy defining pulse are generated separately, was found to improve the image quality considerably.

Assessment of image quality of optical systems.

Abstract: Spot diagrams and the synthesized images of the Siemens star object obtained by an image synthesizer in which the above spot diagrams obtained on a cathode-ray tube were used as the light sources, were compared with the aberration curves and the optical transfer function of the same manufactured lens. The comparison was performed on several field angles and image planes. Systematic comparison of these results gives us versatile information about the image quality of the lens and enables us to understand the mutual relations existing between them. For instance, spurious resolution and heavy deterioration of the images were observed on the synthesized images when there were negative components in the transfer function. Also, it was found that there was an intimate relation between the above defects of images and the spread of the spot diagrams. Next we set the model lenses based on the above one. In these model lenses, certain aberrations were intentionally altered slightly from the initial values without changing the other aberrations. As for these model lens systems, comparisons similar to the above were performed in order to examine the effect and the way each aberration contributed to image quality.

Performance Characteristics of the Digital Autofluoroscope

Abstract: The performance characteristics presented in this paper are: (1) the characteristics of gamma photon imaging with the Digital Autofluoroscope, (2) the resolution and efficiency of multihole and pinhole collimators, (3) a quantitative discussion of the image distortion inherent in pinhole collimators and of the penetration of the pinhole edges. In this discussion, it is pointed out that the various correction modes available, such as normalization of stored data and background suppression, are a means of removing the image distortion evident with pinhole collimators and of restoring image quality loss due to penetration of septa and pinhole edges. Also discussed is the use of the pinhole collimator as a means of magnifying small organs and minifying large ones.

Coronary arteriography. Devices for the improvement of the cineradiographic system.

Abstract: The various elements through which an image is transmitted for final diagnostic viewing are highlighted, with emphasis on the following points: 1. 1. The level of radiation must be such that sufficient statistical data are present in the x-ray image. This is accomplished by grid switching in the x-ray tube working on a constant potential power source. 2. 2. The signal-to-noise ratio in the x-ray image is kept high by means of a good collimating system and by using as small a focal spot as possible. 3. 3. The x-ray image is converted to a high quality light-image by choosing a high gain, high solution image amplifier. 4. 4. Resolution is optimized by use of a variable focal length system that records an image magnified to a degree in keeping with the desired field of view. This makes visible fine vessel detail that otherwise would be lost in the grain structure of the film. The present image quality at the image amplifier output phosphor is such that optical magnification beyond three times produces little or no increase in fine vessel visibility because of the grain structure and scintillation pattern of the image amplifier. To some extent the scintillation pattern can be reduced by increasing radiation to the patient. As indicated in the Appendix, we believe that a reasonable optimum has been selected for the currently available components. The work presented here deals with only a few of the steps by which a cineradiographic system can be improved. We recognize that there are other areas for improvement which will be investigated in the future.

The measurement of radiograph image quality

Abstract: A practical and theoretical study has been made of image quality indicators (IQI's) as detectors of variations in contrast and definition in radiographic images. Among the designs of IQI tested, a simple step type has been found suitable for evaluating the significance of changes in contrast, and a double-wire type, or ‘duplex’, suitable for evaluating definition. In order that an IQI may provide the maximum information about radiographic techniques, it is considered that con- trast and definition should be measured separately. It is shown that for independence of image contrast when measuring definition, platinum wire elements are required in the radiography of steel. With megavolt radiation, still higher contrast is required, increasing the thickness of the platinum elements by a factor of about three compared with 400kV radiation.

Finite Image-Error Theory Based on the Diapoint Configuration*

Abstract: A method is proposed for analyzing the diapoint spot diagrams instead of the spot diagram in one or more image planes. This analysis leads to the consideration of only three typical errors for an off-axis point, which could be called spherical aberration, asymmetry, and deformation. An analysis of a large number of system types by Hildebrand leads us to suggest a simplification of the evaluation, in which we choose as reference the sagittal focus instead of the center of gravity, and the principal ray instead of the best straight line. This enables us at one glance to investigate the image analysis as a function of the aperture.

A 35 mm camera for cineradiology.

Abstract: Film image quality in cineradiology is influenced by many factors (Campbell, Klatte and Shalkovski, 1960). Severe limitations are imposed by the image intensifier which has limited capacity to resolve fine detail. Definition is dose-dependent. As dosage is increased, resolving power of the tube improves and scintillation is minimised. A liberal attitude to radiation levels received by the patient will result in better motion pictures though dose-rates may approach those used in radiotherapy. While the image produced on the output phosphor of the amplifier tube is a poor one by optical standards, it can be de-graded further in transference through the optical systems and camera onto film. Film, film size and processing are important and have been considered elsewhere (Klatte, Campbell and Lurie, 1959). Camera design has not received the same consideration although, together with the projector, it has a profound effect on the depiction of motion (Hood, 1966). With a view to improving existing apparatus, bot...

Objectives for image converters and image intensifiers.

Abstract: The design of objectives for image tubes is discussed with consideration given to the limited resolution of the tubes, the desired resolution in the object plane, and the desired field of view. Particular attention is given to the case of maximum quantum yield for given resolution and field of view. The design of a mirror objective is based on a spherical concave mirror as the main mirror and a plane mirror as the secondary.

An on-line image processing system

Abstract: The high-speed digital computer has contributed to significant progress in the field of optics. One particular area of optics benefiting from this progress is image processing. The purpose of image processing is to aid the human observer in extracting from an image information which has been obscured by some type of degradation The numerous factors which can degrade the quality of an image in an optical system include lens aberrations, poor focus, image motion, turbulence, and diffraction. In general, the problem of obtaining good images in an optical system should be approached by minimizing these factors by careful design and by control of conditions during recording of the image, usually on photographic film. However, there are times when all factors cannot be controlled sufficiently so that the recorded image lacks the required detail for a given application. In the past little could be done in the way of improving the image once it had been recorded. Now, recently developed processing techniques allow the image to be improved after it is recorded. Although there are several different methods by which these improvements can be made, one of the most powerful and flexible utilizes the digital computer. The purpose of this paper is to describe the basic method of processing, the difficulties facing the image processor working on practical problems, and a unique image processing system devised to overcome these difficulties.