Showing papers on "Image quality published in 1984"

Noise Reduction in Image Sequences Using Motion-Compensated Temporal Filtering

Abstract: Noise in television signals degrades both the image quality and the performance of image coding algorithms. This paper describes a nonlinear temporal filtering algorithm using motion compensation for reducing noise in image sequences. A specific implementation for NTSC composite television signals is described, and simulation results on several video sequences are presented. This approach is shown to be successful in improving image quality and also improving the efficiency of subsequent image coding operations.

Two-dimensional filtering of SPECT images using the Metz and Wiener filters

Abstract: Presently, single photon emission computed tomographic (SPECT) images are usually reconstructed by arbitrarily selecting a one-dimensional ''window'' function for use in reconstruction. A better method would be to automatically choose among a family of two-dimensional image restoration filters in such a way as to produce ''optimum'' image quality. Two-dimensional image processing techniques offer the advantages of a larger statistical sampling of the data for better noise reduction, and two-dimensional image deconvolution to correct for blurring during acquisition. An investigation of two such ''optimal'' digital image restoration techniques (the count-dependent Metz filter and the Wiener filter) was made. They were applied both as two-dimensional ''window'' functions for preprocessing SPECT images, and for filtering reconstructed images. Their performance was compared by measuring image contrast and per cent fractional standard deviation (% FSD) in multiple-acquisitions of the Jaszczak SPECT phantom at two different count levels. A statistically significant increase in image contrast and decrease in % FSD was observed with these techniques when compared to the results of reconstruction with a ramp filter. The adaptability of the techniques was manifested in a lesser % reduction in % FSD at the high count level coupled with a greater enhancement in image contrast. Using anmore » array processor, processing time was 0.2 sec per image for the Metz filter and 3 sec for the Wiener filter. It is concluded that two-dimensional digital image restoration with these techniques can produce a significant increase in SPECT image quality.« less

Image reconstruction from frequency-offset Fourier data

Abstract: Motivated by the ability of synthetic-aperture radar and related imaging systems to produce images of surprisingly high quality, we consider the problem of reconstructing the magnitude of a complex signal f from samples of the Fourier transform of f located in a small region offset from the origin. It is shown that high-quality speckle reconstructions are possible so long as the phase of f is highly random. In this case, the quality of the reconstruction is insensitive to the location of the known Fourier data, and edges at all orientations are reproduced equally well. A large number of computer examples are presented demonstrating these attributes. Methods for improving image quality are also briefly discussed.

An Effective Algorithm for Extracting Serial Endocardial Borders from 2-Dimensional Echocardiograms

Abstract: An effective image processing algorithm for extracting the endocardial border from a series of 2-dimensional echocardiograms (2D echo) is proposed. The main steps involved in this algorithm are coordinate transformation, regional co-occurrence matrix thresholding, search region limiting, border detecting, and spatial and temporal smoothing. Using these steps, some major difficulties related to 2D echo image processing including low signal-to-noise ratio, echo drop out, and gray level intensity variability have been dramatically reduced. All endocardial borders in an entire cardiac cycle are computed. This is done automatically on the basis of observer-drawn outlines at end systole and end diastole. These outlines facilitate the quantitative analysis by defining a range in which both boundary dimension and shape changes should occur. Image processing is restricted to this range. The validation studies have been perfonned on test balloons where both image quality has been changed and complex motion abnormalities have been experimentally produced. Good results have also been obtained in patient studies.

A comparison of physical image quality indices and observer performance in the radiographic detection of nylon beads

Abstract: Although various models have been proposed in an attempt to predict the usefulness of a radiographic image in terms of its physical characteristics, no previous work has shown whether a single physical image quality index, such as a signal-to-noise ratio, can reliably predict the performance of a human observer over a broad range of image characteristics. We studied the relationship between physical and visual image quality for the task of detecting nylon beads in radiographs. Thirty-seven imaging cases with different combinations of physical image characteristics were considered; these included variations in object size and magnification, X-ray beam quality, screen-film system, screen-film contact, film density and illumination, and viewing distance. For each imaging case, visual image quality was quantified in terms of observer performance in a 2AFC visual detection experiment. Physical image quality indices were calculated according to eight different models of the detection process; these indices combined data regarding object size and attenuation, screen-film system MTF, film gradient, noise Wiener spectrum, and visual system response. The results of this work indicate that, for the conditions studied, human observer detection performance most closely resembles that of a sub-optimal statistical decision process.

A modified video camera for measuring body image distortion: technical description and reliability.

Abstract: Previously employed techniques for the measurement of body image are briefly described, with a short consideration of methodological or procedural limitations associated with each technique. A new procedure is described which employs a simple modification to a standard video camera to produce an image which appears from 20% thinner to 40% fatter than the actual person, without other distortion of the image. Reliability and preliminary validity data for the new procedure are presented.

The Influence of Front-End Hardware on Digital Ultrasonic Imaging

Abstract: Les systemes d'imagerie ultrasonore dependent des transducteurs de l'electronique de controle pour la generation des impulsions d'irradiation pour la detection des echos reflechis et la conversion des donnees en forme numerique

Method of satellite operation using synthetic aperture radar addition holography for imaging

Abstract: A method of satellite operation utilizing a paired-satellite configuration in which one satellite illuminates the imaged field of view and the other satellite receives the reflected energy using bistatic synthetic radar. This method enables the unambiguous detection of radar signals for imagery construction, improves stability for image quality, provides recording format linearity to minimize image reconstruction processing, provides orthogonal range-doppler pattern distribution at all points in the recording plane to minimize computer processing, provides a triangulated signal reference baseline to improve system calibratability, and enables conformal mapping and uniform sampling of zone plates to achieve three dimensional holography.

Negative working diazo color proofing method

Abstract: This invention relates to negative photosensitized sheet constructions which, upon exposure to an actinic radiation source through a screened image, can accurately reproduce said image. The construction is useful as a color proofing film which can be employed to predict the image quality from a lithographic printing process.

Ultrasonic computed tomography of the breast. Improvement of image quality by use of cross-correlation time-of-flight and phase-insensitive attenuation measurements.

Abstract: The authors present two methods of reducing refraction artifacts in ultrasonic computed tomography of the breast. Measuring the time of flight of sonic pulses by cross-correlation instead of leading-edge detection significantly reduces distortion and improves resolution in speed-of-sound images. Phase-insensitive reception of pulse energy across a large aperture array is shown to be superior to a conventional single-element transducer for attenuation imaging.

Fluoroscopy in children: low-exposure technology.

Abstract: A fluoroscopic system was modified to achieve a 95-98% reduction in radiation exposure and dosage to patients compared with other systems that reduce fluoroscopic radiation dosage. This reduction was accomplished by custom selection of a high conversion-factor, triplemode image intensifier; custom design of a variable-dose rheostat, allowing maximum operator control of video camera gain; installation of an erbium rare-earth beam filter on the x-ray tube; and addition of a digital noise reducer (recursive filter). A total of 1,577 fluoroscopic examinations has been performed on this system, with excellent results. Contrast resolution was increased, while spatial resolution was maintained. Noise (quantum mottle) has been reduced by the addition of a digital image processor. Advantages of the ultra-low-dose system include: all fluoroscopic work is performed in a smooth, continuous real-time mode; the radiation exposure and dose saving is significantly greater than with pulsed and other proposed low-dose fluoroscopic systems; and the system automatically adapts for the wide variation in patient size routinely encountered in pediatric and adult radiology. The image quality is now such that this system could be used routinely for both adults and children.

Magnetic resonance imaging systems: optimization in clinical use.

Abstract: Magnetic resonance (MR) imaging confronts the user with a large number of options that can critically affect image quality. Among the most important parameters over which the user may exercise control are receiver frequency, tip angles, imaging and compensatory gradient strengths, the number of signals averaged, the number of phase encoding gradient steps, and the repetition times. All of these parameters were systematically varied and optimal values determined for a 0.5T Teslacon system, a task which employed both phantoms and normal volunteers. Under the normal conditions of tuning, the z-compensatory gradient presents the most critical adjustment. The compromise between image quality and time of study was also carefully examined, with the following determined as best: 192 gradient steps plus two signal averages for the head coil, or 192 gradient steps plus four signal averages for the body coil.

Optimal Filtering of Radiographic Image Sequences Using Simultaneous Diagonalization

Abstract: A method is presented for the processing of temporal image sequences to enhance a desired process and suppress an undesired (interfering) process and random noise. Furthermore, the processed information is contained in a single frame which is easily interpreted. The method consists of collecting information about the desired and interfering processes from the frames of the given image sequence. The information is in the form of vectors that characterize the temporal properties of the processes. Matrices are formed by performing outer product expansions on these vectors and an eigenvector matrix is found which will simultaneously diagonalize these matrices. By calculating the inner product of a selected eigenvector from this matrix with the image sequence, an enhanced image of the desired process is obtained. A parameter can be adjusted which will increase the amount of suppression for either random noise or the interfering process. At one limit setting of this parameter, a matched filter for the desired process results, while at the other extreme, very high attenuation of the interfering process will occur. Simulations which demonstrate the effectiveness of this technique are presented along with results obtained by processing a radiographic temporal image sequence.

Applications Of Physiological Human Visual System Model To Image Compression

Abstract: Over the past ten years many mathematical models of the human visual system (HVS) have been proposed for image processingapplications.1 -8 It has become clear that incorporating factors accounting for human perception can significantly improve overall picturequality. The purpose of this paper is to address the importance of applying the HVS model to image processing. In order to obtain good image quality at low bandwidth, it is proposed that a physiologically -based HVS model be incorporated with image compression systems. The physiological model needs no adjustment for input image as is required in the psychophysical model.Rationales relating the HVS model to image processingThree major rationales have been recognized for applying the HVS model to image processing. First, image bandwidth compressionrequires a basic understanding bf the HVS. For example, the eye compresses the image before sending visual signals to the brain.There are about 120 million rods and 7 million cones, which collect signals falling on the retina, but there are only 1 million optic nervefibers carrying signals out of ganglion cells to the brain.9 Furthermore, the eye can respond to scenes under background illuminationsthat range over nine orders of magnitude, while the impulse rate measured on optic fibers of the macaque monkey can vary only twoorders of magnitude.10 By treating image signals the same way as human vision is treated, it seems reasonable that better compressioncan be expected. For example, by incorporating the HVS model into the spatial transform coding technique, Faugeras7 has successfullycompressed color images from the original 27 bits /pixel to only 1 bit /pixel. With a better HVS model and a better image coding techni-que, we may be able to compress images at rates less than 1 bit /pixel.Second, human observers eventually judge the quality of processed images. So, it is important to find a good computable fidelity

Comparison of digital focus criteria for a TV microscope system

Abstract: Existing focusing methods, such as standard deviation of gray values, gradients, information content of the image and the lateral inhibition function, were compared, and a new combination criterion was developed. This combined method consists of using the standard deviation of the image for coarse focusing followed by a modified form of the lateral inhibition for the fine focus. The lateral inhibitor model of the eye is a recursive filter that can be simplified to a nonrecursive filtering algorithm, as postulated by Rechenberg. The reported focus method operates over a focusing range (z-axis) of +/- 300 micron and is accurate within +/- 0.1 micron in the transmission, dark-field, and phase contrast microscope.

Image display device

Abstract: PURPOSE:To form a display image having high image quality by forming the visible image for display by an image forming means in the predetermined region of an endless belt-like image carrier and setting the length of the image carrier used for forming and displaying said one image at an integer fraction of the overall length of said carrier. CONSTITUTION:When a writing operation by exposing is started, a photosensitive body 8 continues to turn at a prescribed speed and the writing operation by exposing is continued as well. The writing by exposing with laser light stops at the same instant when the writing by exposing of the area part corresponding to the area of a window hole 3, i.e., an image area is completed, but the body 8 continues to turn until said body arrives at the display position. When the image region where a toner image is formed comes under the hole 3, said region is detected to stop the body 8. The visible image on the body 8 is displayed through the hole 3 in this stage. The length of the belt moved by such one operation is set at an integer fraction of substantially the overall length of the belt so that the belt makes approximately one turn when the cycle for formation of n-pieces of the images and displaying the same is repeated.

Fascimile communication system with desired image quality

Abstract: A facsimile communication system, in which a coding level of a facsimile signal is determined for each image to be transmitted by a coding algorithm of an encoder in correspondence to an image quality of a receiving image sent from the receiving side of the facsimile signal, so that the above-mentioned each image is encoded in the encoder by the use of the coding level and then transmitted to the receiving side.

The information spectrum as a measure of radiographic image quality and system performance

Abstract: The spectrum (spatial-frequency component) of the information capacity of a radiograph, which the authors call the information spectrum, is offered as a measure of image quality and system performance. The information spectrum is a much more practical expression than information capacity by itself: it combines synthetically the contract, the latitude, the sharpness and the granularity, and is expressed as a function of spatial frequency. The information spectrum can be readily calculated by using the dynamic density range and the MTF and noise Wiener spectrum at medium density range. A practical example is given. The appropriate system for each object can be selected by comparing the information spectral values of various imaging systems at the significant spatial frequency range predetermined for each object.

Image Shift, Phase Distortion and the Optical Transfer Function

Abstract: The linear term in the phase transfer function merely produces a bodily shift of the image: only the nonlinear terms affect image quality. A ‘contracted’ form of the transfer function is therefore ...

Videofluorography: the role of temporal averaging.

Abstract: Videofluorography is the technique of obtaining radiographic images by photographing with a multiformat camera the television images produced during x-ray image intensified fluoroscopy. This technique of producing images has received considerable clinical use, but the radiation exposure used has been in doubt. Experiments were performed to evaluate this radiation exposure. It was found that the imaging chain was reducing mottle by temporal integration. These results were tested by comparing the image quality of videofluorographs with that of photofluorographs . The blurring effect of motion on images was also evaluated as this is a factor which must be balanced against the improvement of mottle due to temporal integration. It was found that exposures used for videofluorography were of the order of 10 microR (2.58 X 10(-9) C kg-1) to the input of the x-ray image intensifier.

Solid-state image pickup device

Abstract: PURPOSE:To reduce the noise generated at a correcting circuit and to increase the S/N ratio of a video signal, by amplifying a video signal including a missing part obtained from a solid-state image pickup device of a color VT camera at the front stage correcting the missing part and attenuating it at the rear stage. CONSTITUTION:The video signal including the missing part obtained from a solid-state image pickup device 11 is amplified into a prescribed level at an amplifier 31. The amplified video signal is corrected for the missing part of the video signal at a correcting circuit 12. The corrected video signal is attenuated to a prescribed level at an attenuator 32 and applied to a signal processing circuit 29 to be a video signal of the prescribed system. The noise generated at the correcting circuit 12 is reduced by amplifying the video signal at the front stage of the correcting circuit 12 and attenuating the video signal at the rear stage. Thus, the S/N ratio of the video signal corrected for the failure is improved and the picture quality is improved.

The dependence of the image quality of holographic real images on the reconstruction geometry

Abstract: The effect of changes in plate orientation on the resolution of holographic real images is studied experimentally. Resolution of 64 line pairs per mm was observed in the reconstructed real image from a hologram (NA 0.12, reconstruction beam angle 11 degrees ). Attainment of this performance required alignment of the plate to within 5 minutes of arc. Calculation of the aberration produced by a change in reference beam angle correlated with observed astigmatism and resolution.

A Summary Measure Of Image Quality

Abstract: The Fourier Transform of a line spread function, the O.T.F., can be accurately approximated by the moments of the line spread function. This relation is used to show that the second moment is an excellent single parameter estimate of a system's M.T.F. The second moment is easy to compute and offers many advantages in determining the performance of asymmetric imagery. The overall performance of the system can be predicted by a single universal image quality template.© (1984) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Digital Reconstruction and Display of Compound Scan Ultrasound Images

Abstract: Absrracr-Ultrasonic image reconstruction can be divided into three areas: scan conversion, pixel value assignment (in compound scan imag ing), and image display. In scan conversion, the method of allocation of image values in pixels not intersected by scan lines has a dramatic effect on the image quality. Use of an appropriate interpolation scheme can greatly improve image quality and at the same time reduce the required tine density and hence increase the frame rate. Peak-detected, averaged, and minimum-detected pixel value assignment lead to dramatically different appearances of the resulting compound scan image. The three methods have different effects on the resolution and on differential diagnosis in clinical conditions. In the display of images formed by the three methods, different postprocessing is required to yield comparable images. This is achieved by an adaptive method based on the required histogram. Results are presented for thereconstruction, assignment, and postprocessing techniques of experimental target studies and clinical data obtained with the U.I. Octoson. The effect of

Imaging system response linearization and shading correction

Abstract: Shading correction of image sensors is a very important operation in visual inspection applications. The generation and application of shading cor-rection with and without imaging system response linearization is discussed and demonstrated. The linearization is achieved by subtracting the dark current image and by applying a look-up table operation. The content of the look-up table is obtained by fitting an analytical function to the measured system response. The linearization enables the shading correction to be a linear operation. The quality of the linearization and the shading correction is evaluated using statistical parameters of the processed images. The results show a substantial decrease in the standard deviation of the gray level distribution of uniform reference images.

Exposure artifacts in raster scanned equalization radiography.

Abstract: The image artifacts characteristic of a scanning chest radiographic system are reviewed. The technique employs a pulsed beam of radiation swept in an overlapping raster pattern that can result in severe ripple and scan line artifacts with improper scanning parameters. A one-dimensional treatment of the scanner geometry shows that the artifacts can be eliminated when the beam width is an integral multiple of interpulse spacing. An extension to a two-dimensional analysis indicates that with the collimator geometries employed, artifact-free images are not possible with a fixed x-ray frequency but can be achieved when a variable frequency source is used. A treatment of the sensitivity for artifact formation shows that with proper choice of scanning parameters sizable errors in beam width can be tolerated without significant artifact formation.

A matrix quantizer for image processing

Abstract: This paper discusses a matrix quantizer design algorithm for image encoding problems. The design algorithm is aimed at producing a codebook of matrices which are, at least, locally optimum with respect to a distortion measure. We have considered the squared error distortion measure in this work and generated codebooks based on a training sequence consisting of a number of pictures of different bit rates. The preliminary results show promise for further work in this direction.

Automatic developing bias control device

Abstract: An automatic developing bias control device for an electrophotographic copying machine in which a document image is led onto a photoreceptor through a lens to form an electrostatic latent image on the photoreceptor and the electrostatic latent image is visualized into a toner image by a developing device, the automatic developing bias control device operating on the principle of detecting the density of the document image by a detecting element disposed inside or outside the optical path, delaying the output detection signal for a predetermined time, and imposing a developing bias potential corresponding to the delayed output detection signal on the developing device to thereby provide copy image quality faithful to the original.

Image quality of an analog radiation therapy simulator-based tomographic scanner

Abstract: The spatial resolution and noise level of images produced by a commercial analog tomographic scanner have been measured and compared to those of imagesreconstructed digitally from projections from the same detector. The full width at half maximum of the line spread function was 3.6 mm for images from the analog scanner and 1.1 mm for the digitally reconstructed images. The standard deviation of the CT numbers over a 10‐cm2 circular area at the center of a large water phantom, calculated as a percentage of the linear attenuation coefficient of water, was 3.5% for the analog images, 15.4% for high‐resolution digital images, and 3.2% for digital imagesreconstructed using a convolution filter which reduced the resolution to that of the analog images. The data contributing to each digital image were fewer than those contributing to each analog image by a factor of 10. The noise level did not depend on tube current in either the analog or the digital images. The utility of this analog device in radiation therapy planning will depend upon whether errors in contour localization resulting from transferring data from diagnostic CTscanners exceed the errors due to its poorer image quality.