Showing papers on "Image quality published in 1972"

New coding technique for computer generated holograms.

Abstract: A coding technique is developed for recording computer generated holograms on a computer controlled CRT in which each resolution cell contains two beam spots of equal size and equal intensity. This provides a binary hologram in which only the position of the two dots is varied from cell to cell. The amplitude associated with each resolution cell is controlled by selectively diffracting unwanted light into a higher diffraction order. The recording of the holograms is fast and simple.

Image quality of the cat eye measured during retinal ganglion cell experiments.

Abstract: 1. The modulation transfer function (MTF) of the dioptrics of fifteen cat eyes was determined. The aerial image, formed by the eye of a standard object (a 0.5-1.0 degrees annulus), was photographed. The transmission of the film negative was measured with a scanning microdensitometer to yield the light distribution within the aerial image. Correcting for the double passage, this experimentally determined light distribution and the known object light distribution were used to obtain the MTF, applying Fourier methods. Each MTF was used to calculate the light distribution within the retinal image of stimuli of various geometry used in experiments on retinal ganglion cells in the same eye.2. When the eye was equipped with an artificial pupil of the same size as that used in the neurophysiological experiments (4.0-4.8 mm diam.) the MTF had fallen to 0.5 at 2.43 c/deg. When the pupil was removed the MTF had fallen to 0.5 at a much lower spatial frequency (1.0 c/deg). This shows that even when one uses an artificial pupil too large to provide optimal image quality there is a vast improvement over using no pupil.3. These image quality measurements were prompted by the need to know the actual stimulus image in experiments on the functional organization of the receptive field, a need exemplified in this paper by a few specific physiological results. The full neurophysiological results appear in the next two papers.

Daily x-ray rounds in a large teaching hospital using high-resolution closed-circuit television.

Abstract: A high-resolution, 875-line camera with optical zooming capable of magnifying original films 0.8–8.0× has been used to project daily x-ray consultation rounds to clinicians at satellites as far away as 305 m (1,000 feet). The operating radiologist can control detail emphasis, edge and gamma enhancement, image polarity reversal, and brightness and contrast. Each satellite has zoom and scan controls. Audio communication between transmitter and satellites is maintained by speaker telephone. Although the system cannot present serial and/or multiple films from a single study simultaneously, its excellent image quality, group-teaching capability, and time saving far outweigh this disadvantage.

Annular field optical imaging system

Abstract: IMAGE-FORMING OPTICAL SYSTEMS (DIOPTRIC, CATOPTRIC OR CATADIOPTRIC) INCLUDE ROTATIONALLY SYMMETRIC IMAGE-FORMING ELEMENTS, AND APPARATUS SELECTING FROM THE IMAGE OF AN EXTENDED OBJECT FIELD FORMED THEREBY A PORTION HAVING ADEQUATE IMAGE QUALITY LYING IN A SEGMENT OF AN ANNULAR ZONE CENTERED ON THE OPTICAL AXIS OF THOSE ELEMENTS. RELATIVE MOTION OF THE OBJECT FIELD AND IMAGE-FORMING ELEMENTS PERMITS RECORDING THE IMAGE OF THE ENTIRE OBJECT FIELD.

Aspects of Imaging and Counting in Nuclear Medicine Using Scintillation and Semiconductor Detectors

Abstract: In the interest of minimizing patient irradiation, while maximizing diagnostic image quality, it is desirable to utilize all of the radiation emerging from the patient. For optimum utilization, it appears to be necessary to allow photons with different energies to contribute to the image with different weights. Optimum weights have been determined for the most common case of noise-limited images, where it is assumed that the weights should be chosen so as to maximize the signal-to-noise ratio. For less noisy images, sharpening may be achieved by assigning negative weights to scattered photons; that is, by scatter subtraction. In general, image formation with multiple weighted channels provides a greater degree of flexibility than is possible with a single channel.

Image quality rating system

Abstract: The sharpness of definition of an image on film may be automatically determined by comparing an original image on film with a perturbation of the same image formed from the original image. Such perturbation is achieved by using a hologram deblurring filter upon which the original image is projected. A photodetector is used to measure the power spectral density first of the original image, then of the deblurred image. As one criterion of the evaluation, the readings from the photodetector are compared and if the original image has a lower amount of high frequency content that the deblurred image then the original image is not a sharp image. If the original image has a substantially larger amount of high frequency content that the deblurred image then the original image is a sharp image.

Variations in human cortical response to patterns and image quality.

Abstract: Selective excitation of the human visual cortex by patterned stimuli was examined in a randomly selected sample of normal adtdts and adults with severe monocular visual loss resulting from childhood strabismic amblyopia. Six of the eight normal eyes showed selective but variable configuration cortical evoked responses (VER, passband 0.2 to 50 Hz.) to patterned stimulation when lenses were used to vary the retinal focus. The remainder of the normal sample also showed response peaks where resolution was maximum, but these were in the signal passband 50 to 500 Hz., previously called the fast occipital potential (FOP). We applied normalizing signals to correct for individual response variations. Statistical proofs indicated that this procedure reduced variability about mean results. Two of the three amblyopic eyes produced no response peak, VER or FOP, at the refractive value for best resolution. A small VER peak was found in one amblyopic subject who had eccentric fixation. Subtraction of mean nonpattern from pattern-evoked signals at optimal refraction disclosed a cortical signal which may be a relatively \"pure pattern\" response. As a clinical aid, the VER and its high frequency correlate, the FOP, appear to provide an objective test of the resolving power of the visual system with accuracy equal to or exceeding 0.5 D. sphere.

Accuracy of holographic images.

Abstract: The purpose of the research described in this Letter is to measure the accuracy of the holographic image of a large object and determine some of the experimental factors that may cause a deterioration of this accuracy. The results apply to either the real or the virtual image, but, since the virtual image is not readily accessible for measurements, our tests were limited to the real image. I t is known that a hologram (unlike a lens) is theoretically capable of producing an exact distortionless image of a threedimensional object. In order to obtain this result, the real image must be produced by the conjugate of the original reference beam. This requirement can be most easily satisfied by using a plane wavefront reference beam. In image formation, the hologram plate itself must be considered as an optical element in the system. The hologram plate is ideally treated as a uniformly thick photographic emulsion placed on a flat plate of homogeneous glass of uniform thickness. For the plane wavefront reference and reconstruction beams the above ideal plate introduces no harmful effects on the image. However, the photographic plates-normally used for holography (649F and 10E70) are not ideal and, as a consequence, do contribute a distortion to the images. The thickness of the emulsion was found to have an average variation of 20%. In addition, the glass substrates were found to have a significant variation in thickness. The principal effect of thie thickness variations on the images can be visualized for the simple case where the emulsion thickness variation is quadratic. e.g., assume the emulsion surface has a convex spherical shape. The emulsion media then acts like a lens in the system that introduces an unwanted magnification into the image. This problem was eliminated by putting the photographic plate in a liquid gate, which closely matched its refractive index to a pair of flat glass windows (Fig. 1). These windows were 2.5 cm thick optical flats and introduced less than one wavelength distortion in a plane wavefront passing through the windows. The index matching liquid was o-xylene. The index match was not perfect (1.506 for the xylene compared to 1.532 for the emulsion) but close enough to reduce significantly the observable emulsion thickness effects on the image accuracy. The hologram accuracy test was made with a linear standard bar as the object. The bar was 5 cm thick and 15 cm high with an over-all length of 1 m. The center of the bar was positioned opposite the center of the 13-cm × 18-cm hologram plate. The angle between the reference beam and the hologram normal was approximately 35°. Two glass reticles were set in ports, 75 cm apart at opposite ends of the bar. Each reticle had a horizontal and vertical cross pattern with 25-μ graduations set 125 μ apart. The ports were tapered front and back to give an un­ obstructed line-of-sight through the reticle to the hologram plate. The precision with which the construction and reconstruction beams can be collimated to give a plane wavefront has a large effect on the hologram accuracy. The plane wavefronts were Letters to the Editor should be addressed to the Editor, APPLIED OPTICS, AFCRL, Bedford, Mass. 01730

High resolution portable holocamera.

Abstract: The design, construction, and testing of a portable hologram microscope are described. The instrument is based on a small, reliable, pulsed ruby laser to avoid the degrading effects of vibration; the instrument weighs 7.9 kg and measures 30.5 cm × 33 cm × 15.5 cm. A magnifying relay lens is used in a design such that resolution is limited by the effects of speckle. These effects can be reduced by incoherent superposition of images from the four independent holograms of each object that are automatically recorded. Resolution is 3–4 μm, field of view is 4.5 mm, and depth of field is 4 mm. Results of measurements on resolution, image quality, image intensity fluctuations, and image signal-to-noise ratio are presented.

The Electronic Camera Used in a Reflection Mode

Abstract: Publisher Summary This chapter provides an overview of the electronic camera used in a reflection mode. This mode of operation has the advantage of extending the spectral range in the ultraviolet and infrared parts of the spectrum when compared with classical transmission-mode image tubes. In the design of a “reflection-mode camera,” it is essential to prevent the screening of the photon flux by the electron receptor. As electrons are confined by magnetic lines of force, one possibility is to incline the accelerating electric field at an angle to the focusing magnetic field in an electromagnetically focused image tube. A model has been built to test the image quality of a reflection-mode camera. This model is operated in the transmission mode knowing that image quality is independent of the mode used. The results obtained with this model are very promising. Several plates have been taken showing a resolution of 40 lp/mm over almost the entire field and a maximum resolution of 90 lp/mm. It seems that the best resolution can be obtained in a direction perpendicular to the plane defined by the electric and magnetic fields.

Procedure for Over-all Lens Evaluation Using OTF Data

Abstract: A method is described for making use of large amounts of photoelectric test data, recorded in the form of OTF curves and filed in computer-accessible form, to evaluate image quality over the field in an arbitrary image plane or to locate an optimum image plane by computer processing of the recorded data. Merit parameters such as the OTF, the predicted photographic resolution, the Strehl criterion, and others, are obtained as over-the-field averages, with arbitrary weighting of information from different parts of the field, and also may be reported from individual field points, in various ways. The method has been tested on a wide-angle aerial photographic objective, and example results for this lens are given. Assessment of the possible utility of such a procedure is based on discussion of the practical feasibility of acquiring large amounts of test data by automated instruments, on the computer requirements and processor time needed, and examples of the variety of evaluation tasks that may be performed, with relative ease once the imagery has been mapped throughout the image space. It is concluded that the method does offer possibilities for practical use and may be a desirable way to utilize directly OTF-type test information, in mass, to facilitate decision making in respect to design, fabrication quality, or individual performance of an actual prototype or production lens.

X-Ray Image Intensifiers: Image Quality and Possibilities for Enhancement

Abstract: Publisher Summary This chapter elaborates the image quality and possibilities for enhancement for x-ray image intensifiers. X-ray image intensifiers have greatly changed and improved the diagnostic methods of the radiologist. In order to achieve improved image quality in X-ray image intensifiers, three techniques were investigated. The tube wall was replaced by a fiber-optic face-plate at the tube entrance. X-ray screens with increased quantum absorption and improved transfer characteristic were used and the electron-optical image surface at the output was made as flat as possible. The background due to scattered X-rays is much lower than in tubes with a conventional face-plate. There is only a small probability that X-rays scattered in the fiber-optic plate reach the screen and excite background light. For several object points on the photocathode, a number of tangential and sagittal electron trajectories were calculated and weighted in accordance with reasonable assumptions as to the distribution of initial direction and energy of the photoelectrons. It is suggested that it is possible to build X-ray image intensifiers of correspondingly improved image quality, provided that the viewing screen and the electron-optics are sufficiently good.

Imaging In Nuclear Medicine With Incoherent Holography

Abstract: The problem of radioisotope imag ing in nuclear medicine is to develop an image containing a maximum of in-formation formed by fly-rays which in turn have been "focussed" by only ap-erture limitation. Gamma-emitting radio-labeled medicinals are designed to be concentrated by certain tissues. Abnormal regions may be indicated by either enhanced or reduced concentra tion of the labeled compound. The distribution of the radionuclides, as revealed by their T-rays (e.g., 140 KeV in the case of 99mTc), may then be the basis for diagnosis not possible with X-rays or other nonsurgical techniques. Because the radiation exposure of the patient must be minimized, the images formed are limited by quantum statistics, and indeed the practical detectors are those which respond to single γ-ray quanta. The image quality available with current techniques is modest by the usual standards of X-ray or light imaging; a 25 cm diameter image field seldom contains more than 1000 resolved image elements. Indeed the total information content is often carried by a total of only 100,000 photons. Examples of isotope images useful for diagnosis are given in Figure 1: (a) a brain containing a tumor, (b) a frame of a cerebral blood flow study, and (c) a pair of adrenal glands. In view of the unique nature of the information gained, even this very modest image quality is invaluable in diagnosis. An illustration of this value is the fact that about 2,000,000 radionuclide diagnoses are now undertaken each year in the U.S.

X-ray image enhancement by least-mean-square estimation.

Abstract: The x-ray penumbra effect, caused by the finite focal spot of an x-ray tube, and inherent sources of random noise are the primary limiting factors regarding radiographic image quality. An attempt has been made to devise an optimum spatial filter, which, when realized in binary form, provides substantive image improvement.

Image quality in telescopes with image motion compensation by secondary mirror control.

Abstract: Image motion compensation by servocontrolled tilt of the secondary mirror is applied in a 40-cm diam f/7.5 Cassegrainian balloon-borne telescope. A tilted-aplanatic configuration is used, i.e., the mirrors are aspherized to render the stabilized image free of third-order coma. A spatial resolution of 2 sec of arc is maintained in the presence of pointing errors up to 10 min of arc. The most important remaining aberrations are third-order astigmatism and fifth-order spherical aberration. For the latter, a general expression is presented that can also be applied to other two-mirror telescopes.

The Use Of Image Quality Criteria In Designing A Diffraction Limited Large Space Telescope

Abstract: Marechal's criterion for diffraction limited performance, based on a Strehl definition of 0.80, is extended to include the effects of image motion and a central obstruction, as well as wavefront error. The properties of the extended Marechal criterion are studied to show how it can be used to establish tolerable levels of wavefront error and image motion, and the maximum permissible value for the central obstruction diameter ratio. The limitations of Marechal's criterion are examined by comparing it briefly to other image quality criteria. The properties of the Ritchey Chretien telescope are described in a form permitting analysis of its image-forming characteristics. The manner in which the choice of telescope design parameters can influence the amounts of wavefront error and image motion and the size of the central obstruction is described. These properties are then used in conjunction with tolerance levels established using Marechal's criterion to show how an image quality criterion can limit the choice of telescope design parameters. Tentative boundary diagrams are presented indicating the probable range of design parameters that can be used for the large space telescope, based on the use of Marechal's criterion.© (1972) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Low noise and good efficiency volume holograms.

Abstract: Techniques for improving diffraction efficiency by bleaching conventional absorption holograms, recorded as silver images, have been widely described. Unfortunately, the reconstructed image quality tends to be degraded by an increase of noise-light. Moreover experiments have confirmed the tendency of the bleached silver emulsions to darken, and consequently holograms get worse after a long exposure to light. Attempts have been made to minimize these effects by handling photographically recorded holograms with different bleaching baths and different procedures. An alternative solution is represented either by the use of techniques that yield final holograms that do not contain silver salts or by the use of different recording materials, such as dichromated gelatinand photopolymers. In this letter we present a simple bleaching-plus-darkening procedure, applied to volume (Lippmann-Bragg) holograms, recorded on Kodak 649-F photographic plates. Our purpose was to obtain a compromise between high efficiency and low noise together with light insensitivity of the final hologram. The diffraction efficiency was improved by means of a salted bleaching bath, while scattered noise and light sensitivity were minimized by a successive darkening bath. A two-steps process similar to the above mentioned is commonly used in photography to intensify negatives. We used a darkening bath that yields a final hologram with density equal or a little less than the original one. The processing steps for Kodak 649F plates, conventionally exposed are:

The Evaluation of the Image Quality of Radio-isotope Scanners and γ-Ray Cameras

Abstract: Publisher Summary This chapter describes the evaluation of the image quality of radioisotope scanners and γ-ray cameras. Image formation-based γ-radiation is different from all other methods, because the radioactive tracer is situated within the human body and this makes the images much more diffuse than those obtained by X-radiation. There is more than one photomultiplier each of them receiving scintillations from the crystal. The detector head is stationary and a sophisticated electronic system is necessary to localize the coordinates of each scintillation. In order to measure the line-spread function at different distances from the detector head, two test objects were used. The first consisted simply of a 30-cm length of 0.8-mm internal diameter plastic tubing filled with radioactive material and the other consisted of a number of 5-cm lengths of the same tubing placed parallel to each other to form a rung-like test object. The modulation transfer function for a scintiscanner and a γ-ray camera derived from their line-spread functions is also analyzed in the chapter.

Modulation Transfer Function Measurements on Channel Image Intensifies

Abstract: Publisher Summary This chapter describes the modulation transfer function (MTF) measurements on channel image intensifiers. The MTF has been increasingly regarded as one of the most important ways of describing image quality. The application of the MTF to a particular type of imaging device is considered and some pitfalls that must be avoided if meaningful measurements are to be obtained are pointed out. If transfer functions are to be applicable to an image transfer process, the necessary conditions for Fourier transformation must be satisfied. The process must be linear in response and spatially stationary. The channel plate consists of a large number of electron multiplier tubes in a hexagonal array. If the pattern that is imaged through the device is limited to low spatial frequencies, the imaging process can be regarded as being stationary over the restricted spatial frequency range involved. The profile of the line-spread function is measured with a scanning microphotometer. The chapter suggests to use the normal subjective criteria of image-quality assessment to supplement the results of linear analysis.

Apollo 9 multiband photography experiment S065

Abstract: Fourier analysis was applied to microdensitometer scans of a selected region of one SO65 frame in each of the three black-and-white bands. The approach was unique because a somewhat arbitrary section of the image was used and not limited to available targets as in edge analysis. Comparison of duplicates and calculation of absolute SO65 MTF were done by applying linear systems theory to the spatial spectra of the image scans. It was found that the duplication process was nonlinear and resulted in general amplification of spatial frequency modulation. However, the increase in modulation was offset by a corresponding increase in the granularity of the copies. The amount of increase seemed to be related to the initial granularity, but a direct relationship was not verified. Band-to-band comparison of image quality was achieved in the form of signal-to-noise ratio curves as a function of spatial frequency for each band. From this standpoint the DD band was an order of magnitude better than the other two. These were several factors that restricted the analysis of the Apollo 9 imagery. Among these were the lack of precise sensitometric and optical system data on the high altitude photography. In addition it was determined that there was only one simultaneous pair of high altitude and SO65 frames. Finally, the original SO65 photography was not available for scanning (for obvious reasons), thus eliminating a reference base for granularity and SO65 MTF determination.

Electron-optical Transfer Functions of Image Intensifies

Abstract: Publisher Summary This chapter discusses electron-optical transfer functions (e.t.f.) of image intensifiers. It expresses the on-axis electron-optical image quality of image intensifiers in terms of the e.t.f., the Fourier transform of the point-spread function. The derivation is restricted to the case in which the imaging electrons move in the vicinity of the optical axis, where the rotational, symmetrical electric and magnetic fields may be approximated by up to second-order terms. In this paraxial region, the Helmholtz-Lagrange law or sine condition holds, which expresses the angle of intersection with the axis at the image plane in terms of the initial energy and angle of emission of the electron. It is concluded that where imaging fulfils the paraxial requirements, the monochromatic e.t.f. gives a quick estimate of on-axis image quality and its sensitivity to variations of design parameters. If the distribution of the initial electron energies is known, it is possible to take two or more values for the initial energy and by applying proper weighting factors to the calculated e.t.f.s to make a better approximation.

Correction of image distortion in the liver scintigram due to the respiratory movement using an on-line computer system

Abstract: Image distortion in the liver scintigram due to the respiratory movement often confuses physicians in its interpretation. An attempt to correct this distortion was described using an online digital computer system. The procedure was as follows: (11 the respiratory movement was sampled by a collimated NaI (Tl) detector positioned beneath the bed seeing the edge of the liver, 12) an original scintigram was divided into five subscintigrams according to the phase of the respiratory curve, having equal total counts in each, 13) the center point of gravity of each sub- scintigram was calculated, (4) the sub-scintigrams were shifted and superimposed so that each center point of gravity fitted to the center of the image. Phantom experiments using a respiration simulator showed sufflcient recovery of the image quality in terms of focal lesion detectability and the smoothness of the edge of organ. Moreover, the actual magnitude of the movement was precisely estimated in a two-dimensional plane using the center point of gravity of each sub-scintigram. Several considerations in application for clinical liver scans were also discussed. Of these, the usefulness of the correction in computer image processing, such as smoothing, was specially stressed. (auth)

A Comparison of Holographic Versus Lens Type Acoustic Image Systems by Computer Simulation

Abstract: Ideal image systems of holographic or lens type should have similar performance, given similar aperture/wavelength ratios. However, practical acoustic image systems introduce amplitude and phase nonlinearities, noise, and geometric distortion at different points in the system. Computer simulation of a holographic and a lens type system of limited aperture/wavelength ratios has been made to emphasize the differences in subjective image quality introduced by such effects as diffraction, undersampling, saturation, and system noise.

The Image Quality of an Image Intensifier Expressed in terms of its Equivalent Quantum Efficiency

Abstract: Publisher Summary This chapter discusses the image quality of an image intensifier expressed in terms of its equivalent quantum efficiency The performance of a detector in recording an optical image can only be fully described when both signal and noise in the image can be specified for an input of any spatial frequency and any spectral content An experiment was carried out in which the granularity of photographic images was measured when using an intensifier over a range of gains These measurements have shown that a further source of granularity can exist in the intensifier because of local variations in intensifier gain, and that under certain conditions these provide the dominant limitation in image quality The result, of a photoelectron leaving the photocathode will follow some probability distribution, which will be independent of its point of origin In the absence of gain variations in the intensifier the number of stored photons at low gains should be determined primarily by the film The gain variations for the brightness distribution for single-photoelectron events are also elaborated later in the chapter