Showing papers on "Image quality published in 1977"

Maximum Entropy Image Reconstruction

Abstract: Two-dimensional digital image reconstruction is an important imaging process in many of the physical sciences. If the data are insufficient to specify a unique reconstruction, an additional criterion must be introduced, either implicitly or explicitly before the best estimate can be computed. Here we use a principle of maximum entropy, which has proven useful in other contexts, to design a procedure for reconstruction from noisy measurements. Implementation is described in detail for the Fourier synthesis problem of radio astronomy. The method is iterative and hence more costly than direct techniques; however, a number of comparative examples indicate that a significant improvement in image quality and resolution is possible with only a few iterations. A major component of the computational burden of the maximum entropy procedure is shown to be a two-dimensional convolution sum, which can be efficiently calculated by fast Fourier transform techniques.

Analysis of halftone dot profile and aliasing in the discrete binary representation of images

Abstract: Screening techniques are widely used in the binary display of continuous-tone images by digital output devices. The quality of the halftone image resulting from such a nonlinear transformation is dependent on the dot profile employed. In the Fourier domain, aliasing degrades the halftone image. The relationship between image quality and dot profile is studied from this point of view. For a well-known dot profile, it is shown analytically how aliasing is suppressed, and that quantization contouring may be eliminated without an appreciable increase in aliasing.

Correction of atmospheric distortion with an image-sharpening telescope*

Abstract: A 30 x 5 cm aperture telescope employing six movable mirrors to compensate for atmospherically induced phase distortion is built and tested. A feedback system adjusts the mirrors in real time to maximize the intensity of light passing through a narrow slit in the image plane. Essentially diffraction-limited performance is achieved when imaging both laser and white-light objects through 250 m of turbulent atmosphere. The behavior of the telescope is accurately predicted by computer simulations. The system has yet to achieve its full potential, but has already operated successfully for objects as dim as 5th magnitude.

Image blur for rainbow holograms.

Abstract: An analysis is presented for selecting the important rainbow-hologram formation-setup parameters for minimization of the image blur.

Rate-Distortion Coding Simulation for Color Images

Abstract: We propose a distortion measure for color images, based on a mathematical model of color vision, and supported by subjective image quality evaluations. The visual model is configured after a simplified schematic of the retina's physiology and it transforms the red, green and blue image components into a representation that is consistent with major psychophysical phenomena. The distortion criterion proposed consists of measuring the mean square error in the above representation space. Consistency of the measure with human quality judgment is supported by a subjective ranking experiment, using images distorted in various ways by addition of noise. An optimal coder (in the rate distortion sense) is also simulated, which minimizes the distortion measured as proposed. The resulting image provides a quality standard at the rate distortion bound, against which actual coders can be compared. Finally it is observed that from a statistical point of view, the model's output is a near ideal color image representation for efficient coding.

Signal transmission system with an error control technique

Abstract: A signal transmission system embodying this invention which can control errors comprises a selective automatic repeat request (ARQ) system for controlling errors occurring in transmission of data on telephone data communication channels. With this selective ARQ system, an error-controlling signal conducted through a backward channel does not contain a check bit for detection or correction of errors, thereby preventing a time loss which might occur if a error-control signal was repeatedly issued between the transmission and receiving sides. The subject signal-transmitting apparatus is adapted to be used in a static image transmission having a large amount of data and has such a circuit arrangement as attains the efficient transmission of data and the display of an error-free image of good picture quality.

Synthetic radar imagery

Abstract: A method for producing three-dimensional isometric images of a conducting radar target from measured ramp response waveforms is tested for the case of nonmutually orthogonal viewing angles. It is found that, in general, image quality is somewhat degraded and several new parameters are introduced, but useful images can still be obtained. Methods for obtaining the new parameters are included as well as other modifications which were developed to enhance image quality. Images of three aerospace-type targets obtained from low frequency scattering data are presented.

Reconstruction of Objects from Their Projections. The Influence of Measurement Errors on the Reconstruction

Abstract: A two dimensional layer of a three dimensional object can be reconstructed by means of a large number of projections through this layer using a convolution technique. The quality of the reconstructed image is limited by noise in the primary projection data. Different sources of noise have been investigated. Their influence on image quality is calculated. Ultimate limits in spatial and density resolution are derived.

Automatic controlling method of image quality in transfer type electrostatic copier

Abstract: PURPOSE: To improve the image quality of copies by measuring the degrees of fatigue of photoreceptor, and automatically controlling charge quantity, exposure and developing bias voltage based on the measurement results thereof. COPYRIGHT: (C)1978,JPO&Japio

Photon Limitations in Imaging and Image Restoration

Abstract: : This report describes progress made in image quality factors, limiting performance of speckle and amplitude interferometry, and formulation of a least-squares filtering problem for space-variant degradations. This work is in photon-limited imaging systems, their limitations, and the restorability of their imagery.

Image quality in mammography.

Abstract: Image quality in mammography is affected by the shape, size, and x-ray absorption properties of the anatomic part or lesion to be radiographed in addition to x-ray beam quality, geometric unsharpness, and the resolution, characteristic curve, and noise properties of the recording system. The authors review x-ray energy spectra, modulation transfer functions. Wiener spectra, characteristic and gradient curves, and radiographs of a breast phantom and a resected breast specimen containing microcalcifications; these factors, and the complex relationship between them, affect image quality and patient radiation exposure. Evaluation of the best system or technique for obtaining a breast image is discussed in terms of the compromise between diagnostic certainty and cost or risk.

Image Noise and Smoothing in Computed Tomography (CT) Scanners

Abstract: The question of what spatial frequency response gives optimum image quality in computed tomography (CT) images is studied. We have developed a technique for smoothing these images by using a modified back projection filter with attenuated high frequency response. The results are images with a blurred appearance but dramatically reduced image noise. On processing raw data from the EMI head scanner in this way, grey and white matter distributions are clearly visualized with no increase in radiation dose. These results are analyzed in terms of the Weiner spectrum and correlation properties of CT noise. In particular, a "noise equivalent aperture" is defined in a way analogous to that of Shade. It is shown that the prediction of the simple Rose model of noise sampling can not explain the improvement produced by smoothing, even when the correlated character of the noise is taken into account.

Transfer method in multichromatic electrophotography

Abstract: PURPOSE: To improve a transferred image quality, by setting the resistivity of belt to a predetermined value in the system where an image of various colors is transferred on the transfer paper being conveyed by the belt. COPYRIGHT: (C)1978,JPO&Japio

Copy picture quality controller of electrostatic copying machine

Abstract: PURPOSE:To perform controlling of developing bias voltages by detecting the illuminances of ground parts and image parts by an image sensor.

Control method for copier image quality

Abstract: PURPOSE:To enhance copy image quality for both originals of characters and a photograph, by discriminating between them and automatically changing copy process conditions. CONSTITUTION:Original 15 is scanned with original density detector 14 comprising illumination lamp 12 and photodiode array 13, its signal is operated via detection circuit 9, operation circuit 10, and control circuit 11, and this signal provided to light source 16 before original scanning to change bias voltage for source 16 in optical system 1. In general, a character original has 2-3 peaks and a photographic original has 4 or more peaks in the graph where X-axis represents image density detction level and Y-axis represents the sum of each level signals number. Therefore, when judged to be a character original, light source bias voltage is raised and when judged to be a photographic origianl, it is controlled to a lower value.

Data conversion unit

Abstract: PURPOSE:To obtain video picture with a good quality in which the picture quality is minimized, by minimizing the data density change of the binary information data before and after the conversion

Prediction Of Realistic Visual Tasks From Image Quality Data

Abstract: As a realistic visual task subjects had to recognize military vehicles out of six. alternatives. Percentages of correct identifications were determined at three different observation distances in order to interpolate the distance required for 50% correct, which is taken as a measure of performance. The scenery was simulated indoors by slide-projection in favour of better control of conditions and faster procedure. The slides were photographed at the location of an earlier field trial. The performance of a. portable, image, intensifier was measured, in this way as a function of luminance and contrast in object space. It ap-pears that recognition of the present set of objects is visually equivalent to the detec-tion. of a circular disk, and can be predicted from image quality data (displayed S/14, MTF) along that line.

Real Time Digital Correction Of Acquisition Errors Applied To Solid State Scanners

Abstract: Capturing an image using a solid state scanner requires focusing the subject image on to the scanner array with some type of lens. Various kinds of degradations occur including Cos4 law, illumination non-uniformity, dust on the optical surfaces and flaws in the imaging array. The combined effects of all sources of image acquisition errors can result in serious cosmetic defects in the resulting image. Dramatic improvements in image quality can be achieved by multiplying the intensity value of each image pel by a correction factor: () Pout = Pin Pmax CFi Pout = corrected pel value Pin = pel value as captured Pmax = maximum possible pel intensity value CFi = correction factor for the ith position on the scan line The correction factors (CFi) are determined by capturing an image of a "standard white material" and calculating the average white value for each position on the scan line. The correction calculation requires multiply and divide operations which are too complicated to be performed at real time (21 million pels/second) in computer software. Therefore a 2-stage tabular lookup procedure has been implemented in bipolar RAM and PROM hardware. An additional feature of the approach is the possibility of performing any arbitrary intensity transformation by the substitution of a different PROM table.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Image Quality In Computerized And Conventional Tomography In The Assessment Of Craniofacial Anomalies

Abstract: New comprehensive surgical procedures for the correction of severe craniofacial anomalies have resulted in a need for precise anatomical information for presurgical planning. The extreme variability in expressivity of these anomalies has served to make this need particularly urgent. This, in turn, has led to requests for increasing numbers of torrographic scans for assessment of these patients. Both standard and computed tomograms are used for this purpose. Unfortunately, there is an extreme paucity of information on comparative radiation dose levels and comparative image quality among these methods and their use may, in some instances, place patients at undue risk. For purposes of the current study, a phantom head was constructed which allowed the measurement of the Threshold Quality Factor (TQP) as a function of radiation dose. Quantitative results obtained from this phantom and from cadaver heads on three CT units (CT/T GE, Delta 50, and EMI 5005) and from one standard tomographic unit (CM Stratomatic) were compared in terms of dosimetry, quantified image quality, and subjective clarity of anatomical landmarks. Based on findings in this study, it is suggested that a diagnostic hierarchy could be formulated which would significantly reduce the total radiation levels to which specific types of patients are exposed.

An Automated Visual Edge Match System For Image Quality Assessment

Abstract: This paper describes a system which automatically matches scene edges to a physical matrix of test edges for the purpose of estimating image quality. The system developed by EIKONIX is based upon the Itek Visual Edge Match (VEM) Station, highly modified to provide the automatic function. Random edge location and identification is performed by the operator. Scanning is accomplished by means of a one-dimensional self-scanned photodiode array coupled to the microscope by an anamorphic optical system. The data is processed internally by means of a unique eigenvector approach which yields an interesting and sensitive quality discriminator. Calibration is automatic, the machine being operated under computer control in one of several modes. Training time is minimal, and the design of the densitometric system is such that many of the common error sources and limits on dynamic range are avoided. The paper includes system design and analytical considerations as well as experimental data.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Comparison Of Translate-Rotate And Pure Rotary Computed Tomography (CT) Body Scanners

Abstract: Two types of fast fan-beam CT body scanners are in widespread clinical use. A bi-modal type employs a series of linear translations followed by rotational steps. Rotary scanners use pure rotary motion of the source and detector or source alone (stationary detector type). We have conducted comparison studies using production models of an EMI-5005 and a GE CT/T installed at the Department of Radiology, U.C.S.F. These include quantitative determinations of noise and resolution, semiquantitative comparisons using phantoms, and qualitative evaluation of CT images obtained from double-scanned patients. Image quality of the two machines is roughly comparable under normal use. The most important differences involve the frequency and character of artifacts. The smoothness and speed of the rotary system's scanning motion greatly reduces that systems sensitivity to patient-motion-related streak artifacts. On the other hand the translate-rotate system currently offers higher spatial resolution and optional slow, high-dose, high-sensitivity scans.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Preprocessing X-Ray Transmission Data in CT Scanning

Abstract: While the reconstruction algorithm utilized in computerized tomography (CT) is important, the overall performance of the system is limited by the quality of the measured transmission data which is used as a basis for the reconstruction process. If the projection values derived from the measured data do not adequately represent the line integrals of the linear attenuation coefficients within the slice being scanned, even a perfect reconstructruction algorithm will give rise to a distorted image. Phenomena which tend to deteriorate the quality of the measured data, and hence the final image, include the effective finite dimensions of the scanning aperture, distortions introduced by the detector system such as afterglow, and nonlinearities related to the spectral distribution of x-ray photons used in scanning. Computer methods of preprocessing the x-ray transmission data to minimize these distortions are discussed and illustrated.

Image Data Processing By Hybrid Sampling

Abstract: Transmission of images over a digital channel in the transform domain can lead to reduced bandwidth requirements. This is a consequence of redundancy reduction as the linear transformation compacts the image energy into a small region. By transmitting the transform components that have the most energy/information, images can be reconstructed at the receiver with negligible degradation in the subjective picture quality and with reduced bit requirements. The criterion for selecting these components is generally based on geometrical zone or magnitude or variance all in the transform domain. Magnitude sampling although adaptive, requires additional bits as their location needs to be specified. Variance criterion, on the other hand, is in general adapted to the average picture statistics, and hence may not be an optimal selection for the specific image being processed. As a compromise between these two, hybrid sampling which considers both magnitude and variance is proposed. This technique is applied to GIRL and MOONSCAPE images which are quantized uniformly to 256 gray levels. Processing is carried out on (16 x16) pixel subimages using discrete transforms such as Haar, Walsh-Hadamard, Hadamard-Haar and discrete cosine. Mean square error (mse) for various data compression ratios utilizing hybrid selection between the original and reconstructed images is computed and is compared with those for the magnitude and for the variance selections. The mse for the hybrid approaches that for the magnitude which shows that the former is an attractive scheme for data compression with significant bit reduction and negligible increase in mse. Various ratios for magnitude-variance selection are being adopted. This may lead to an optimal ratio in terms of bit rate, mse and image quality.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Simple Method of Describing the Photographic Image Quality

Abstract: If the conclusions which Kondo et al. [1] obtained by testing a large number of photographic lenses (35 mm cameras) are combined with the quality number suggested by Heynacher [2] a very simple method of describing the photographic image quality is achieved. This method, its origin, and some results are discussed.

Film-screen sharpness in complex motion tomography.

Abstract: An unsharp radiologic image is created in tomography by the combined motion of the x-ray tube and the film-screen cassette. This image is generally recorded at angles other than normal to the film-screen plane. A metbd for determining the influence of this recording angle on film-screen sharpness is described. The method involves imaging an edge target at various angles between the x-ray beam and the film-screen plane. The MTF is then calculated from the edge images. The effect of film-screen sharpness and quantum noise on subjective image quality in temporal bone tomography is discussed.

Reduced scale image input device

Abstract: PURPOSE:To prevent non-uniform image quality by subjecting an original picture to scanning from two light sources from the center of the original picture towards two ends at a gradually loer speed.

[Image quality in film and xero-mammography. I. Rendering of low contrast values (author's transl)].

Abstract: The rendering of low contrast values by various mammographic imaging systems was investigated by a semi-objective procedure. Test exposures of a line raster with variable line widths were evaluated visually. Significantly better results were achieved by a xero-radiographic method. This was better than non-screen mammographic film in terms of object size, lower sensitivity to scatter and better resolution. The use of a tungsten rotating anode, with about 0.5 mm. Al filter, in xeromammography provided a satisfactory compromise between image quality and radiation dose in the rendering of low contrast studies.

On-line digital image restoration and manipulation using a minicomputer.

Abstract: A digital image processing system using a minicomputer that has the capability to make on-line digital image processing has been developed. By use of this system image restoration of motion blurred images due to uniform linear and rotating motion has been carried out in the space domain with the aid of the idea of man–machine feedback. To restrain extreme noise amplification during the restoration process, the technique of smoothing and differentiation of the data based on a method of least squares has been applied. A new technique to manipulate the low contrast image is also demonstrated by which the processed image is observable with better appearance than that of the unprocessed one. In this manipulation, the human visual system has played an important part in complementing discarded image information.