Showing papers on "Image quality published in 1971"

Image processing

Abstract: Image processing techniques find applications in many areas, chief among which are image enhancement, pattern recognition, and efficient picture coding. Some aspects of image processing are discussed--specifically: the mathematical operations one is likely to encounter, and ways of implementing them by optics and on digital computers; image description; and image quality evaluation. Many old results are reviewed, some new ones presented, and several open questions are posed.

Image Coding by Adaptive Block Quantization

Abstract: A new source encoder called the adaptive block quantizer is proposed for coding data sources that emit a sequence of correlated real numbers with known first- and second-order statistics, Blocks of source output symbols are first classified and then block quantized in a manner that depends on their classification. The system is optimized relative to both the mean square error and the subjective quality of the reconstructed data for a certain class of pictorial data, and the resulting system performance demonstrated. Some interesting relationships between mean square error and subjective picture quality are presented.

Reconstructing 3-D Specimens From 2-D Section Images

Abstract: Reseachers seeking a histological determination of microscopic specimen morphology face the basic problem of analyzing three-dimensional microscopic specimens with two-dimensional imaging devices. This tedious task can be done at the microscope but reproduction of images in hard copy or digital form entails the loss of depth information. Quantitative measurements must generally be made on 2-D images. Several methods have been proposed and implemented to obtain and display 3-D images. In this paper we discuss an approach combining digital image processing techniques with stereo display techniques. This allows control of image quality and selection of different 3-D characteristics for display.

A New Approach to the Evaluation of Radiographic Systems

Abstract: The design of radiographic systems supposes the existence of objective evaluation methods. Such methods can generally be divided into two classes: (1) sensitometry, and (2) image quality evaluation.The comparative study of the merits of black-and-white and colour radiographic systems requires more general evaluation methods.The method used in our laboratory is essentially an adapted visibility test, organized in such a way as to permit a precise objective interpretation.The results obtained thus far are now being correlated with a comprehensive image quality criterion, based on our actual knowledge of vision, on the image transfer theory and on a decision theory.This criterion contains all important characteristics of the radiographic system, including the human visual sense. As an example, this evaluation method is applied to the Medichrome system and the results are briefly discussed.

Nonredundant Arrays and Postdetection Processing for Aberration Compensation in Incoherent Imaging

Abstract: For incoherent imaging systems, wave-front aberrations can have the effect of severely reducing the contrast of high spatial frequencies. Although postdetection image processing can improve image detail, the success of such an approach is limited by image noise. If a simple spatial filter consisting of a nonredundant array of clear openings in an opaque mask is placed in the pupil plane of the system, postdetection image processing yields a restored image superior to that obtainable from a system without the pupil-plane filter. Experimental results confirm the predictions of the theory.

Clinical tests on a prototype semiconductor gamma-camera

Abstract: A prototype γ-camera has been constructed from a slice of lithium-drifted germanium 44 × 44 mm in area and 6·5 mm in sensitive thickness. Positional information is obtained using the orthogonal strip principle, the inherent spatial resolution being 3 mm. Data are presented on energy resolution, uniformity, linearity of image and spatial resolution. The application to imaging distributions of 99Tcm in rats and humans is demonstrated, and comparisons on picture quality and background made (using the identical sources) with a conventional Anger system.

Primary x-ray dodging.

Abstract: By using compensating filters which can be optically aligned in the beam, radiographic image quality is increased, the dose to the patient is reduced to approximately one-half, and film costs are reduced accordingly. The improvement in image quality is the result of compensation for the varying thickness of the object and reduction in background fogging due to reduced scattering.

Status of OTF in 1970

Abstract: The concept of the assessment of image quality by means of the optical transfer function (OTF) is traced from the early use of sine wave test charts through to the development of the high precision...

A measure for radioisotope scan image quality.

Abstract: Summary A measure of scan quality has been developed by making quantitatively comparable the effects of statistics and blurring. Strictly speaking, the model has been shown to be useful for some two-tone patterns only, but because locally scans approximately reduce to such patterns, we can expect the measure to be generally applicable. This measure is useful in the specification of clinical scanning parameters and also in providing a framework in which to consider the design of scan processing methods.

Noise Characteristics of Bragg Imaging

Abstract: The effect of Brillouin scattering on the image quality of a Bragg-imaging system is analyzed in this chapter. The particular Bragg-imaging system considered here uses a cylindrically convergent illuminating light beam. The signal-to-noise ratio for an image element (that is, a resolution cell) is shown to vary with the image-plane location when the image sensor is broadband in temporal frequency. It is also shown that quantum noise due to light scattered from thermal phonons (Brillouin scattering) is the dominant limiting source of noise for a Bragg-imaging system operating in the ultrasonic band at room temperature when the best available TV camera tube is used for detecting the image. Competing noise sources which are evaluated include quantum noise due to signal photons and image sensor noise. The effects of dust particles and other inhomogeneities on scattered light are not considered.

Image quality in radiography

Abstract: This paper discusses the problems of obtaining a precise and uniform specification of image quality for different radiographic methods of inspection. Recommended standards are also discussed.

Digital Video Systems Applied To Product Inspection

Abstract: A real-time, digital, video processing system offers a flexible means for performing high-speed, on-line, automated product inspection. With the capability to digitize and store a 512 x 512 multi-gray level image in 1/30 second as well as subtract a reference image from a new image in a TV frame time, it is possible to perform high-speed inspection of parts, packages and labels. Such a unit can operate as a stand-alone unit or as a pre-processor for a dedicated or time-shared computer. Design trade-offs and examples of specific applications will be discussed.

Image Quality in Sampled Data Systems

Abstract: : The paper deals with aliasing, an important effect of one-and two- dimensional sampling on image quality. Aliasing changes the normal criteria of utility of the modulation transfer function (MTF) as a measure of system quality. Aliasing can be eliminated by letting the MTF fall to zero at one-half the sampling frequency. This, of course, markedly reduces the signal-to-noise ratio at the display (SNR(D)) near cutoff and thus reduces operator performance. Several factors control the amount of information an observer extracts from an image and the rate at which he extracts it. The paper presents the results of a series of experimental programs relating observer performance to the modulation transfer function area (MTFA) and to the SNR(D) and derives the relationship between MTFA and SNR(D). The paper discusses the tradeoffs as they are presently understood.

Evaluation of Direct-View Imaging Devices

Abstract: Image-intensifier devices have traditionally been evaluated by a somewhat subjective estimate of performance in terms of output picture quality, particularly limiting resolution of the output image as seen by a human observer, as a function of input image illumination. To translate these subjective impressions into quantitative data, both to spectify tube performance objectively and to identify the factors which govern performance as a guide to corrective measures, workers have agreed on several quantitative measurements of image-intensifier performance. Most important are measurements which determine the sensitivity, in terms of the brightness gain and the contrast degradation in the device due to background,* and the resolution performance of the device. Following Perrin,1 we believe limiting resolution is completely unsatisfactory as a measure of resolution performance, and have standardized on the modulation transfer function to describe image-intensifier resolution performance.

Fiber Optics, XIV. Statistical Evaluation of Fiber-Optics Imagery*†

Abstract: The mean-squared error between an object and image formed by scanning was used by Beall as a measure of the degree of fidelity of the image. A similar approach to the image transfer by fiber optics is presented. In this paper, the one-dimensional line-scan analysis proposed by Beall is extended to encompass a two-dimensional sampling process for evaluating the image transfer in a fiber bundle. Interesting results occur when the evaluation technique is extended to the comparison of the imaging properties of a static bundle and a bundle that is dynamically scanned. This analysis indicates that there is a significant difference of resolution between the static case and the dynamically scanned case. The difference is found to be largely determined by the fiber configuration within the bundle. Experimental results in the case of the static fiber will be presented.

Relative Effects of Gaussian and Poisson Noise on Subjective Image Quality

Abstract: Photographic transparencies were prepared with precisely determined quantities of gaussian (signal-independent) and Poisson (signal-dependent) noise and submitted to observers for subjective ranking of image quality. Average values of noise and signal-to-noise ratio, based upon the relative variance of the signal, were calculated for the imagery: (a) assuming equal a priori probabilities of allowed signal levels; (b) using a normalized probability density function for signal levels derived from scene statistics. Best correlation with the results of subjective quality ranking was obtained with an average signal-to-noise ratio based upon the normalized probability density function.

Resolution factors in edgeline holography.

Abstract: When an in-line Fresnel hologram of an object such as a projectile in flight is made, the reconstruction comprises an image of the outside edge of the object superimposed upon a Fresnel diffraction pattern of the edge and an unmodulated portion of the reconstruction beam. When the reconstructed image is bandpass filtered, the only remaining significant contribution is that of a diffraction pattern which is symmetrical about an edgeline gaussian image of the object. The present paper discusses the application of this type of holography in accurately locating the edge of a large dynamic object, the position of which is not accurately known in any dimension. A theoretical and experimental analysis was performed to study the effects of motion, hologram size, film type, and practical limitations upon the attainable resolution in the reconstructed image. The bandlimiting effect of motion is used to relate the motion effected resolution limit of holography to that of photography. The study shows that an edgeline can be accurately located even at high velocity normal to the edge.

Calculation of the Optical Effects of a 27.5-m Spherical Mirror.

Abstract: People standing under a large spherical mirror see the world inverted, hanging above them as a real image. The shape of this image world depends upon where on the floor the observer stands. In this paper formulas for calculating image positions as a function of observer position are derived and depicted in diagrams of typical image worlds. The images formed by light reflecting several times in the mirror are also calculated. There are both an erect real image world and doubled rings of inverted images surrounding the single-reflection image world.

Radiological Imagery Enhancement

Abstract: Radiological images constitute an important source of diagnostic information in medical practice. The radiological images presently available to the medical profession generally suffer from low contrast and poor resolution. Many factors contribute to the poor image quality. Some of them are inherent in the nature of the object and the basic radiological imaging process and some of them are due to imperfections or degradations of the system. In the past, little could be done in the way of restoring or enhancing the image once it had been recorded. Now, recently developed techniques allow the image to be made more intelligible to the human observer by correction or compensation of the degradations which it has undergone. Based on the knowledge of some identifiable characteristics of degrading influences and some known characteristics of the object, these techniques perform a sophisticated mathematical operation on a recorded image to undo the effects of whatever degradations may be present and restore, as nearly as possible, the image which would have been recorded in the absence of degradation. They correct various geometrical, photometric and spatial frequency distortions. Sometimes, even with a perfectly recorded or restored image the information content cannot be fully extracted or retrieved because of the limitations of human vision. Image processing techniques will allow the image to be purposely distorted in frequency domain and/or gray levels to suppress background, to emphasize some special features, etc.© (1971) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Imaging with Low-Redundancy Arrays

Abstract: A conventional imaging system, consisting of a collection of lenses or mirrors with clear apertures, provides non-uniform coverage of the spatial spectrum of an incoherent object1,2 Stated another way, a certain spatial-frequency redundancy is inherent to such a system, with low spatial frequencies being weighted more heavily than high spatial frequencies In this paper we propose that it may sometimes be desirable to destroy this redundancy by inserting a complicated mask in the exit pupil of the system, thereby allowing the images to be formed with a multi-element interferometer With a proper choice of mask geometry, the spatial frequency redundancy can be minimized or eliminated The destruction of redundancy will be shown to be advantageous if the optical elements are aberrated and if post-detection image processing may be applied to improve image quality We emphasize at the start that all arguments to follow apply only for spatially incoherent objects