Showing papers on "Image quality published in 1981"

A Survey of Electronic Techniques for Pictorial Image Reproduction

Abstract: This paper is a tradeoff study of image processing algorithms that can be used to transform continuous tone and halftone pictorial image input into spatially encoded representations compatible with binary output processes. A large percentage of the electronic output marking processes utilize a binary mode of operation. The history and rationale for this are reviewed and thus the economic justification for the tradeoff is presented. A set of image quality and processing complexity metrics are then defined. Next, a set of algorithms including fixed and adaptive thresholding, orthographic pictorial fonts, electronic screening, ordered dither, and error diffusion are defined and evaluated relative to their ability to reproduce continuous tone input. Finally, these algorithms, along with random nucleated halftoning, the alias reducing image enhancement system (ARIES), and a new algorithm, selective halftone rescreening (SHARE), are defined and evaluated as to their ability to reproduce halftone pictorial input.

The role of human visual models in image processing

Abstract: The mechanisms are discussed by which the human eye forms a neural image of the outside world for transmission along the optic nerve. Mathematical models of these mechanisms which can be exploited for engineering purposes are presented and their usefulness and limitatious are discussed. Three areas in which human vision models have been successfully applied are image bandwidth compression, image quality assessment, and image enhancement; results from these areas are summarized and some example results are given. Some future directions are suggested.

Computer Architectures for Pictorial Information Systems

Abstract: In the international search for the optimal image processing computer architecture, image parallelism is the key to cost effectiveness.

Physical and Technical Considerations of Computerized Fluoroscopy Difference Imaging

Abstract: Considerations for the optimum design and use of a computerized fluoroscopy apparatus for performing time dependent image subtraction are presented. The advantages of logarithmic processing are presented. Assuming such processing, the interrelationship of achievable signal to noise, dynamic range and the minimum number of grey levels needed to digitize each image is discussed, and a formula relating these three quantities is derived. Image quality limits imposed by noise sources not associated with the detected x-ray fluence are discussed and a criterion for choosing a maximum x-ray fluence which will not waste patient dose is presented. The limits to spatial resolution achievable with conventional image intensifiers are discussed and it is shown that the maximum one dimensional spatial resolution in the object plane is achieved when the magnification of the x-ray system is such that the image of the x-ray focal spot projected through a point in the object plane onto the detector plane just covers the width of two pixels. The effect of the detection of scattered radiation on the difference image is discussed and it is shown that a conventional scatter reduction grid will improve image quality only if the ratio of the number of detected scattered photons to the number of detected primary photons is greater than 0.8 when no grid is used.

All Solid State Color Camera With Single-Chip Mos Imager

Abstract: An all solid state color camera using a solid state image sensor has many advantages over the conven- tional tube type camera, such as light-weight, low power consumption, high reliability, elimination of lag and high picture quality.

A Pinned Sine Transform Image Coder

Abstract: The pinned sine transform (PST) coder described is a practical approximation to the pinned KLT coder. The image is partitioned into two fields: a boundary field, which depends only on the coded block boundaries, and a pinned field, which vanishes at the boundaries and is subsequently sine transformed and compressed. The reconstructed image is continuous across the block boundaries and "blocking effects" are hardly visible. Simulation results are given for fixed and adaptive compression schemes with fair image quality at low bit rates down to 0.3 bits/pel.

Image subtraction with an encoded extended incoherent source

Abstract: A technique of encoding an extended incoherent source for image subtraction is presented. The source encoding is obtained from the coherence requirement for image subtraction operation. Since the coherence requirement is a point–pair concept for image subtraction the encoding can take place by spatial sampling an extended incoherent source with narrow slit apertures. The basic advantage of the source encoding is to increase the available light power for the processing operation, so that the inherent difficulty of obtaining a very small incoherent source can be alleviated. Experimental results obtained with this encoded incoherent source are given. Comparisons with the results obtained by processing technique are also provided.

X-Ray diagnostic installation

Abstract: In an exemplary embodiment, radiography and fluoroscopy is carried out by a film cassette, an image intensifier television chain and a circuit for the automatic influencing of parameters determining the x-ray image quality, which circuit exhibits a radiation sensor, and a comparator for the comparison of a nominal setpoint value with the actual value delivered by the sensor, in which analog to digital converters are provided for the formation of an electric signal corresponding to the electrode voltages of the x-ray image intensifier, which electric signal is supplied in the form of an address to a memory in which the dependency of the conversion factor of the x-ray image intensifier upon the electrode voltage is stored. In addition, a converter is provided for the formation of an electric signal which is dependent upon the aperture of the x-ray collimator, which electric signal forms the address for a memory in which the dependency of the background of the x-ray image intensifier upon the aperture of the collimator determining the image format is stored. The output signals of the two memories are superimposed in an adder on the nominal setpoint value for the control loop.

Iterative image restoration considering visibility

Abstract: A new algorithm for iterative image restoration based on the least-squares criterion, which can provide a restored image with a good appearance for a human observer, is proposed. The introduction of a nonlinear constraint matrix, which is determined by taking account of features of an input image or an intermediate processing result, solves the problem in image restoration of obtaining a result without serious deterioration of local space details and discernible noise for human eyes. It is also evident in the course of derivation of the algorithm that the procedure defined as reblur serves to suppress noise amplification in the sense of the least-squares criterion as well as to ensure convergence of the solution. Suitability of the proposed algorithm is confirmed through experiments of iterative restoration for an image degraded with a Gaussian point-spread function with noise.

Narrow beam light transfer in small particles: image blurring and depolarization: erratum

Abstract: Narrow beam light transfer in a layer of small particles is treated theoretically in terms of degradation of image quality and depolarization. Computer simulations using Monte Carlo methods are described, and some results of the simulations are shown. Simulations were done for cases in which a ground-based linearly polarized light beam is transmitted to a spacecraft through cloud layers, and the light is detected on the spacecraft. Image degradation and light depolarization resulting from transmission through clouds are shown qualitatively and quantitatively. The results indicate that depolarization is negligibly small, but degradation of image quality is not negligible, especially when the light beam divergence is large. At infrared wavelengths the effect of image blurring is much smaller than at visible wavelengths.

Intensity Mappings: Linearization, Image-Based, User-Controlled

Abstract: The objective of intensity mappings, functions from recorded intensity to displayed intensity, is to provide contrast in the display of features of interest in images where these features appear as regions of increased or decreased intensity. Three component objectives of such mappings can be identified: 1) device linearization, 2) emphasis of contrast in commonly occurring and accurately measured intensities, and 3) user-controlled mapping based on the importance of image features. Mappings of type 1, which immediately precede the display device, are designed to modify the device so that equal changes in the driving intensity value are equally perceivable. The importance of this mapping will be demonstrated, and the argument that by itself this mapping must improve displayed image quality will be refuted. A method of measuring the JND curve and of calculating this mapping from it will be discussed. A method for automatic determination of a mapping of type 2 consisting of a nonstationary modification of Cormack's mean pixel uncertainty minimization method [Phys. Med. Biol. ^(2)] will be presented. Methods for user control in the determination of mappings of type 3 will be briefly discussed.The ProblemThe display of intensity-varying images is a common requirement in such diverse areas as medicine, astronomy, and satellite imagery, to mention just a few. These images are two- dimensional distributions of a single intensity variable, and features to be seen are areas of increased or decreased intensity. The images are created by a detection device or by an image processing or construction system and are first recorded as a two-dimensional distribution of some nonviewable intensity variable such as the density distribution of silver on film, the electrical time signal which can drive a video display, the track of magnetic strength on videotape, or the array of numeric intensities in a computer memory. We call this original "image" the recorded image and its intensity variable the recorded intensity. The purpose of a display system is to transform a recorded image into an image viewable by a human in such a way that features of interest are detectable and characterizable and draw the observer's attention. The recorded intensity serves as a driving intensity for the display system, which transforms this driving intensity into a viewable intensity.We are concerned here with the performance of displays in transmitting contrast in recorded intensity, as opposed to their performance in transmitting spatial information as measured by properties such as resolution and geometric distortion. The images with which this paper is concerned are not ordinary pictures of scenes directly viewable b> tue eye but rather those like infra-red images of the earth and diagnostic medical images v.nich are made by measuring the two-dimensional distribution or projection of some physical parameter. With these images the objective is to discern abnormal increases or decreases in intensity, but unlike ordinary pictures of scenes, there is no concern for realism in the display of these images.Display devices have been developed to present these images using various mechanisms for presentation and various scales of viewable intensity. Among the presentation mechanisms have been visible display on a CRT, electrostatic plotting, film exposure by movable light sources, and film exposure by CRT. Among the viewable intensity scales have been grey- scale, half-tone, various pseudocolor scales, and apparent height, as well as various combinations of these.Given a viewable intensity scale, a critical choice determining the quality of display of a recorded image is of the mapping between recorded intensity and viewable intensity. The objective of the mapping is to transmit sensitively that contrast in the recorded image which contains the information required by the observer. It is with this mapping that this paper is concerned. The paper is an attempt to provide a clear framework in which the mapping can be designed and chosen.Strictly speaking, the intensity mapping that we wish to optimize is that between recorded intensity and intensity perceived by the viewer. As diagramed in figure 1 this mapping consists of three consecutively applied mappings: first, the mapping that we

Subjective Evaluation Of A Perceptual Quality Metric

Abstract: A major problem which has plagued image processing has been the lack of an effective image quality measure. It is well known that common measures which are mathematical and analytically tractable do not correlate with human subjective evaluation. This paper presents the results of a subjective evaluation on twelve versions of a black and white image (the SPIE GIRL) and the rank ordering obtained with three computational measures. It was found that a measure based on a model of the human visual system compared to the subjective evaluation with a correlation of .92.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Scanning type image recorder

Abstract: PURPOSE:To eliminate the thinning-down of image and achieve the improvement in the image quality of characters by changing the width of the image signal in an apparatus of a system by which nonexposed parts are visualized. CONSTITUTION:A character code signal is applied to a terminal 1, from which it is inputted as the series signal of a signal line 9 into a processing circuit 10, by which it is inverted to an inverted signal 501. This signal is further applied as the signal 502 of an expanded pulse width DELTAt to a beam modulator 53. Here, if the visualizing level is defined as 504 when the inverted signal 501 is used straightly as a modulating signal, a width 505 is obtained. When the signal 502 is used as a modulating signal, the position where a scanning spot is produced moves from 511 to 512 and therefore, the exposure distribution becomes as shown by solid lines in 504 and the width to be visualized becomes 506. If the scanning speed of the scanning spot is defined as Vs, the length of the segment extends by Vs.DELTAt. Because of this, the thinning-down of the images may be eliminated and the image quality may be improved.

Image-sharpness criterion for space-variant imaging

Abstract: Image-sharpness criteria studied previously have depended on the assumption of the spatial stationarity of the point-spread function of the degrading medium plus the imaging lens system. If this assumption does not hold, the sharpness criteria no longer necessarily reach their extrema when system aberrations are zero. A criterion has been constructed that avoids this dependency, although at the expense of requiring information that is unnecessary in the spatially stationary case. After the instantaneous degraded image is filtered with a transfer function that is equal to or slightly greater than the transfer function of the degrading medium, the resulting image must be equal to the long-term-averaged image. The instantaneous image before modification is therefore diffraction limited or almost diffraction limited. The criterion may be applied locally.

Effects of Wobbling Motion on Image Quality in Positron Tomography

Abstract: The design of any positron emission tomograph involves some compromises. In particular, the simultaneous goals of high sensitivity and good resolution have resulted in circular ring systems using relatively large crystals and rotation/wobbling motions. The wobbling motion unfortunately results in nonuniform linear sampling. In this paper we investigate the effect of wobble diameter and number of wobble positions on reconstructed image quality. Computer simulations were performed with noise-free and Poisson noise projection data. For the best choice of wobble parameters, image artifacts were less than 1% and the noise level was increased by less than 5%. Noticeably worse performance was obtained when using some parameters suggested by others.

Effects Of Mirror Surface Ripple On Image Quality

Abstract: Mirror surface ripple acts as a phase grating to diffract light out of the central maximum of the point spread function (PSF), reducing image quality. The effects of ripple on image quality are examined with the aid of computer simulations using rotationally symmetric wavefront error models, and through interferometric measurements of a mirror known to have significant surface ripple. Image quality is evaluated in terms related to the performance requirements of large orbital astronomical telescopes that must perform in both ultra-violet and visible light. Techniques for measuring and specifying ripple are discussed.

Patient dose and image quality in computed tomography

Abstract: The relation between radiation dose in neurologic computed tomography scanning and image quality is described. Three different sets of images were obtained at varying exposures and were quantitatively evaluated by a panel of neuroradiologists. Anatomic information in the image varied with exposure. The relation of image quality and dose conforms to previous theoretical results and suggests that an optimal exposure level can be established.

Image quality in holography with a pseudorandom diffuser

Abstract: It is well known that the Fourier transform hologram is suitable in principle for achieving high storage density. In practical applications of this holographic system, various types of diffusers have been studied to increase recording re­ dundancy and to decrease spatial noise in the reconstructed image. The development of the pseudorandom diffuser (PRD) realized the Kanji generator with holographic storage of the Kanji (Chinese ideograms) of over 5000 kinds. The fundamental features of the PRD have been analyzed, but the performance of these PRDs was discussed in terms of a 1-D optical system, and the effects of the object pattern on the image quality were neglected. In this Letter the performance of PRDs in a holographic imaging system with Kanji charac­ ters is evaluated by computer simulation of 2-D Fourier transform holography. Table I shows three kinds of phase sequences of the dif­ fusers discussed here, which are four-level pseudorandom, six-level complexed pseudorandom, and two-level random phase sequence as a reference for the former two cases. If we let the respective sequences be { 1, 2 . . . , ,...} (0 ≤ i < 2π), the characteristic of each sequence is expressed in terms of the constraint: i i+1 becomes either 0 or Π with equal

Color solid image pickup device

Abstract: PURPOSE:To prevent a false color signal generated in a specific color signal by performing multiplication by a coefficient when calculating a color signal from a signal read by a solid image picture element so that vertical substantial sensitivity distribution on the image pickup surface will nearly be symmetric. CONSTITUTION:A signal read out of color image pickup element 25 is delayed by one horizontal scanning period (1H) delay line 26 and subtracted from the output signal of element 25 by subtracter 29 to obtain color signals R and B. Those color signals are delayed by one-bit delay line 30 and then added to the last color signal by adder 31 to obtain signal R. This signal R is further delayed by 1H delay line 38 by 1H added to the output of adder 31 by adder 39 to obtain sinal R, which is applied to process circuit 34. the processing circuit for the signal R is added to make a coefficient for calculating output signal R vertically symmetric. Consequently, luminance signal Y outputted from adder 27 is never influenced, so that the picture quality will be improved as much as the false color signal disappears.

Microprogrammable Ultrasonic Image Processor And Its Applications To Image Manipulation

Abstract: A microprogrammable ultrasonic image processor and its applications to image enhancement are presented. An image processor has been implemented to input, manipulate and display the ultrasonic image data with a high image quality and also to facilitate the human operation. Although this processor has specially designed circuits for ultrasonic image processing, a microprocessor and its associated arithmetic circuits can be utilized for programmed image manipulations; for example, smoothing, enhancement, contrast stretching, area/arc-length measurement and so on.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Synthetic Aperture Radar (SAR) Image Quality Considerations

Abstract: Characteristics of radar scattering, the 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 are specified which relate to application information requirements and associated measurement techniques are presented.

An Improved Electro-Optical Image Quality Summary Measure

Abstract: The operational performance of electro-optical imaging systems is currently predicted using models based on an approach introduced by Johnson in 1958. This model has been shown to be inadequate when used to predict performance over a wide range of conditions of signal-to-noise ratio and range to the target. This paper describes our efforts to develop and validate a model which is more effective than the Johnson model in predicting image quality. Implications in performance prediction modeling and electro-optic sensor design tradeoffs between sensitivity and resolution are also discussed.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Image quality control in the Meteosat Ground Processing System

Abstract: The various aspects of Meteosat image quality control are considered User requirements on the quality of end-products (mainly meteorological products) and on the image quality are presented, showing how image errors contribute to the total error budget Methods of evaluating the various measures of image quality are briefly outlined and the implementation of these methods within the Meteosat Ground Computer System is critically reviewed The need for a close coupling between mission control and payload quality control is emphasized The observed quality of the imagery from the first flight model (F1) of Meteosat is also discussed

Solid-state image pickup element plate

Abstract: PURPOSE:To obtain a high-quality image signal, by setting random one of the area, the form and the arrangement of the picture element in an image pickup element plate to secure a uniform distriution of the space frequency of a picture element arrangement pattern and to suppress the occurrence of a moire phenomenon at a specific frequency. CONSTITUTION:A solid-state image pickup element plate consists of a red signal extracting photodetector R, a green signal extracting photodetector G and a blue signal extracting photodetector B. The form and the size are set constant with the arrangement pattern set random for each picture element. The area or the form are set random when the arrangement pattern is set constant. Thus the space frequency distribution is set uniform for each picture element pattern, and the occurrence of a moire phenomenon is suppressed at a specific frequency along with suppression of the local peak. Then the deterioration of picture quality such as the occurrence of a false color signal, a reduction of image resolution, etc. can be avoided.

A two-chip imaging system for OCR applications

Abstract: Presents a two chip imaging system for optical character recognition (OCR) applications. It consists of a 64/spl times/24 photodiode array providing directly a binary pattern. The image quality is enhanced by means of a separate signal processing chip which performs centering of the image and delivers control signals for further on-line character recognition. The two chips are part of a fully integrated OCR wand.