Showing papers on "Image quality published in 1985"

Second-generation image-coding techniques

Abstract: The digital representation of an image requires a very large number of bits. The goal of image coding is to reduce this number, as much as possible, and reconstruct a faithful duplicate of the original picture. Early efforts in image coding, solely guided by information theory, led to a plethora of methods. The compression ratio, starting at 1 with the first digital picture in the early 1960s, reached a saturation level around 10:1 a couple of years ago. This certainly does not mean that the upper bound given by the entropy of the source has also been reached. First, this entropy is not known and depends heavily on the model used for the source, i.e., the digital image. Second, the information theory does not take into account what the human eye sees and how it sees. Recent progress in the study of the brain mechanism of vision has opened new vistas in picture coding. Directional sensitivity of the neurones in the visual pathway combined with the separate processing of contours and textures has led to a new class of coding methods capable of achieving compression ratios as high as 70:1. Image quality, of course, remains as an important problem to be investigated. This class of methods, that we call second generation, is the subject of this paper. Two groups can be formed in this class: methods using local operators and combining their output in a suitable way and methods using contour-texture descriptions. Four methods, two in each class, are described in detail. They are applied to the same set of original pictures to allow a fair comparison of the quality in the decoded pictures. If more effort is devoted to this subject, a compression ratio of 100:1 is within reach.

Human image understanding : Recent research and a theory

Abstract: The perceptual recognition of objects is conceptualized to be a process in which the image of the input is segmented at regions of deep concavity into simple volumetric components, such as blocks, cylinders, wedges, and cones. The fundamental assumption of the proposed theory, recognition-by-components (RBC), is that a modest set of components [ N probably ≤ 36] can be derived from contrasts of five readily detectable properties of edges in a 2-dimensional image: curvature, collinearity, symmetry, parallelism, and cotermination. The detection of these properties is generally invariant over viewing position and image quality and consequently allows robust object perception when the image is projected from a novel viewpoint or degraded. RBC thus provides a principled account of the heretofore undecided relation between the classic principles of perceptual organization and pattern recognition: The constraints toward regularization (Pragnanz) characterize not the complete object but the object's components. A principle of componential recovery can account for the major phenomena of object recognition: If an arrangement of two or three primitive components can be recovered from the input, objects can be quickly recognized even when they are occluded, rotated in depth, novel, or extensively degraded. The results from experiments on the perception of briefly presented pictures by human observers provide empirical support for the theory.

A Visual Model Weighted Cosine Transform for Image Compression and Quality Assessment

Abstract: Utilizing a cosine transform in image compression has several recognized performance benefits, resulting in the ability to attain large compression ratios with small quality loss. Also, incorporation of a model of the human visual system into an image compression or quality assessment technique intuitively should (and has often proven to) improve performance. Clearly, then, it should prove highly beneficial to combine the image cosine transform with a visual model. In the past, combining these two has been hindered by a fundamental problem resulting from the scene alteration that is necessary for proper cosine transform utilization. A new analytical solution to this problem, taking the form of a straightforward multiplicative weighting function, is developed in this paper. This solution is readily applicable to image compression and quality assessment in conjunction with a visual model and the image cosine transform. In the development, relevant aspects of a human visual system model are discussed, and a refined version of the mean square error quality assessment measure is given which should increase this measure's utility.

Effect of noise correlation on detectability of disk signals in medical imaging

Abstract: Pixel signal-to-noise ratio is one accepted measure of image quality for predicting observer performance in medical imaging. We have found, however, that images with equal pixel signal-to-noise ratio (SNRp) but different correlation properties give quite different observer-performance measures for a simple detection experiment. The SNR at the output of an ideal detector with the ability to prewhiten the noise is also a poor predictor of human performance for disk signals in high-pass noise. We have found constant observer efficiencies for humans relative to the performance of a nonprewhitening detector for this task.

Theoretical optimization of dual-energy x-ray imaging with application to mammography.

Abstract: Detection of a target object in a radiological image is often impeded by an obscuring background "clutter" resulting from the contrast between various materials in the neighborhood of the target. Dual-energy techniques can reduce or remove this clutter. In order for the target to be detectable in the image after dual-energy processing, the signal-to-noise ratio (SNR), defined as the difference between the target and the background divided by the photon noise in the difference, must exceed some threshold. A given SNR may be obtained for a wide range of the energies of the two x-ray beams and the ratio of their fluences. A theoretical model is developed which permits the choice of beams to be optimized with respect to some critical parameter--in this case, patient dose. The analysis is applied to the detection of calcifications in mammography. For an ideal imaging system, we predict that the optimum beam energies are 19 and 68 keV. A dose of 0.42 cGy is required to obtain an SNR of 5 for detection of a 0.02-cm cubic calcification in the resulting clutter-free image. This can be reduced to 0.16 cGy if the higher energy image is smoothed, prior to dual-energy processing, such that its variance is reduced to one-fourth of its unsmoothed value.

Reconstructing 3-D light-microscopic images by digital image processing

Abstract: A reconstruction procedure based on linear system theory has been developed for 3-D light-microscopic images. Inverse filtering with the 3-D optical transfer function was used for image reconstruction. The procedure allows a significant improvement in spatial resolution in the image planes perpendicular to the optical axis.

ECG-synchronized cardiac MR imaging: method and evaluation.

Abstract: An electrocardiographic (ECG) sensing and gating device compatible with a 0.35-tesla (T) magnetic resonance (MR) imager has been developed and used to produce 802 MR images of the heart in 30 patients. The instrument consists of an isolated acquisition module, an electrically floating preamplifier, and a monitor gating module. Two spin-echo images were acquired for each of five, 0.7-cm thick, transaxial sections from the base to the apex of the heart during each ECG-synchronized imaging run. Image quality was assessed in a blind study by two investigators, on a scale from 0 to 3, as diagnostic [2-3] or nondiagnostic [0-1]. There was agreement in 91.4% of their assessments of diagnostic images (68.1% of the images studied). Resolution of heart anatomy on the MR images was adversely affected by prolonged spin-echo time delay, imaging in late diastole, image acquisition at the cardiac apex, irregular triggering, and artifacts. The synchronization of gradient pulses to the ECG at 0.35 T appears safe for patients, permits diagnostic resolution of images, allows image acquisition at distinct points during the cardiac cycle, and enables monitoring of patients during imaging.

Image gathering and processing - Information and fidelity

Abstract: In this paper we formulate and use information and fidelity criteria to assess image gathering and processing, combining optical design with image-forming and edge-detection algorithms. The optical design of the image-gathering system revolves around the relationship among sampling passband, spatial response, and signal-to-noise ratio (SNR). Our formulations of information, fidelity, and optimal (Wiener) restoration account for the insufficient sampling (i.e., aliasing) common in image gathering as well as for the blurring and noise that conventional formulations account for. Performance analyses and simulations for ordinary optical-design constraints and random scences indicate that (1) different image-forming algorithms prefer different optical designs; (2) informationally optimized designs maximize the robustness of optimal image restorations and lead to the highest-spatial-frequency channel (relative to the sampling passband) for which edge detection is reliable (if the SNR is sufficiently high); and (3) combining the informationally optimized design with a 3 by 3 lateral-inhibitory image-plane-processing algorithm leads to a spatial-response shape that approximates the optimal edge-detection response of (Marr's model of) human vision and thus reduces the data preprocessing and transmission required for machine vision.

Removal of image intensifier veiling glare by mathematical deconvolution techniques

Abstract: X-ray images acquired with an image intensifier detector system suffer from veiling glare, a low-frequency degradation described by a point spread function (PSF). The PSF has two experimentally determined parameters unique to a given image intensifier. This information is utilized to deconvolve the degradation from digitally acquired images. Results demonstrate a significant increase in contrast ratio of high-contrast objects after deconvolution and image restoration.

Projection Space Iteration Reconstruction-Reprojection

Abstract: Recently, an iterative reconstruction-reprojection (IRR) algorithm has been suggested for application to limited view computed tomography (CT). In the IRR, the interpolation operation is performed in the object space during backprojection-reprojection. The errors associated with the interpolation degrade the reconstructed image and may cause divergence unless a large number of rays is used. In this paper, we propose a projection space iterative reconstruction-reprojection (PSIRR) algorithm based on backprojection-reprojection in the projection space. In the process of the backprojection-reprojection, iteration is performed with a single equation instead of multiple equations and interpolation is eliminated. Computer simulation results are presented, and image quality of the PSIRR algorithm shows a substantial improvement compared to the original IRR algorithm. In addition, the new algorithm was applied to ultrasonic attenuation CT using a sponge phantom.

Enhancement of SPECT images by Fourier filtering the projection image set.

Abstract: Tomographic images from rotating gamma camera systems are often difficult to interpret because of poor contrast and high noise levels. A method is presented for improving the quality of these images by Fourier filtering the projection image set prior to reconstruction. A two-dimensional circularly symmetric Gaussian function is used as the spatial frequency filter. This filter can be optimized to enhance contrast and suppress noise in the projection image set in a straightforward and simple manner from the power spectra of representative projections. Preprocessing of the projections makes it possible to use a ramp reconstruction filter. The resulting tomographic sections show a dramatic improvement in image quality.

Image quality improving process and apparatus and sheet usable therewith

Abstract: An apparatus, a process and a processing sheet for improving qualities of an image in sharpness, density and/or glossiness. A copy or printed sheet having an image is coated with a thin sheet at the image bearing side of the copy. The copy is then pressed together with the thin sheet, and simultaneously heated so as to soften or fuse at least the surface of the image on the copy. Then, the sheet is peeled off the image after the image is cooled sufficiently. Surprisingly, the qualities of the image are improved as compared with the image before processing.

A new digital tomosynthesis method with less artifacts for angiography

Abstract: A new nonlinear reconstruction method for tomosynthesis is described. This method is suited for ‘‘dilute’’ objects, i.e., objects in which most of the voxels have negligibly small absorption. Images of blood vessels filled with contrast material approximate this condition if the background is subtracted. The technique has been tested experimentally using a wire phantom and a prepared human heart. The results show significantly less artifacts than the well‐known backprojection. It is possible to get diagnostic image quality with a few projections. The reconstruction algorithm can be realized with dedicated real‐time hardware.

Image Quality: Measures and Visual Performance

Abstract: Analysis, research, and recommendations regarding the image quality of displays have come from a variety of disparate sources, intended for a wide variety of applications and uses. These sources of data include those which mathematically describe images for purposes of determining analog system requirements, as in commercial and closed-circuit television; the encoding studies which are designed to minimize transmission and storage bandwidth; and the psychophysical studies which attempt to relate physical measures of the image to what the user or observer believes to be “image quality” in a utility sense. It is not surprising that persons with academically and scientifically different backgrounds have performed these many and diverse studies, and it is similarly not surprising that there is a general lack of familiarity of results from one segment of the research and engineering community to the next.

Triangular Spect System for 3-D Total Organ Volume Imaging: Design Concept and Preliminary Imaging Results

Abstract: SPECT systems based on 2-D detectors for projection data collection and filtered back-projection image reconstruction have the potential for true 3-D imaging, providing contiguous slice images in any orientation. Anger camera-based SPECT systems have the natural advantage supporting planar imaging clinical procedures. However, current systems suffer from two drawbacks; poor utilization of emitted photons, and inadequate system design for SPECT. A SPECT system consisting of three rectangular cameras with radial translation would offer the variable cylindrical FOV of 25 cm to 40 cm diameter allowing close detector access to the object. This system would provide optimized imaging for both brain and body organs in terms of sensitivity and resolution. For brain imaging a tight detector triangle with fan beam collimation, matching detector UFOV to the head, allows full 2? utilization of emitted photons, resulting in >4 times sensitivity increase over the single detector system. Minification of intrinsic detector resolution in fan beam collimation further improves system resolution. For body organ imaging the three detectors with parallel hole collimators, rotating in non-circular orbit, provide both improved resolution and three-fold sensitivity increase. Practical challenges lie in ensuring perfect image overlap from three detectors without resolution degradation and artifact generation in order to benefit from the above improvements. An experimental system has been developed to test the above imaging concept and we have successfully demonstrated the superior image quality of the overlapped images. Design concept will be presented with preliminary imaging results.

An approach to specifying a minimum dose system for mammography using multiparameter optimization techniques.

Abstract: Analytical expressions have been written for image quality in mammography. Multiparameter optimizations have been conducted to find mammographysystems providing the lowest patient dose for a given image quality. The optimizations are subject to constraints imposed by technology, such as power limits on the tube focal spot, absorption efficiency related to detector resolution, and others. The optimizations permit system geometry, kVp, filtration, detector resolution, focal spot size, and grid characteristics to vary simultaneously and self‐consistently subject to the constraints. A system configuration approaching a factor of 3 dose reduction has been found without assuming radical technological advances. The system satisfies image quality constraints for both large and small targets and would be possible to implement clinically. The sensitivity of the results to the assumptions made in the modeling has been investigated.

Image transmitting system having density selection

Abstract: An image transmitting method in an image transmitting apparatus such as a facsimile apparatus having a plurality of transmission modes in which pixel densities differ. This method comprises the steps of: detecting a size of a recording paper on the reception side; detecting a size of an original to be transmitted; automatically selecting the transmission mode of a high pixel density in the case where the size of the transmitting original is larger than the size of the recording paper; transmitting the image of the transmitting original to the reception side; and detecting the receivable mode on the reception side. With this method, even in case of reproducing the image in the reduction size mode on the reception side, the image with a high image quality can be always derived irrespective of the selection of the image quality mode of the operator.

Image reconstruction from coded data: II. Code design.

Abstract: A strategy is given for the design of coded apertures with respect to a given class of objects that are to be imaged. Previous knowledge of the first- and second-order statistics for the object class is assumed. The object class is characterized by its Karhunen–Loeve eigenvectors and eigenvalues, whereas the imaging system is characterized by its singular-value decomposition. We introduce the concept of alignment in which the aperture parameters are adjusted until the system is tuned to measure the given object class well. A mean-square-error figure of merit that indicates degree of alignment is given, and alignment is performed by standard optimization techniques. We illustrate this technique with a simple proof-of-principle experiment. These concepts are general and may be applied to any linear imaging system.

Vectorgraph coding: efficient coding of line drawings

Abstract: A method for the efficient coding of line drawings is discussed. The intent is to provide an extremely low bandwidth representation for images, preserving “intelligible” image content but not necessarily image quality. This has led to an image transformation involving edge enhancement, detection, line thinning, and polygonal splining which is termed the polygonal transformation . The graph-like image which results from this transformatiom is coded quite efficiently by using vectorgraph coding , which codes a series of vectors in a manner similar to that used in many computer graphics systems. This technique has been applied to a body of images of American Sign Language and the results are encouraging.

Method and apparatus for improving quality of energy subtraction image

Abstract: In energy subtraction processing, two or more stimulable phosphor sheets are used to record radiation images of an object which includes bone image and soft tissue image, and a difference signal for forming an image wherein the bone image or the soft tissue image is erased is obtained from the radiation images The image quality of the energy subtraction image is improved by using the difference signal for picture elements at the portion where the bone image or the image of the soft tissue of a thickness of a predetermined value or larger is present, and by using the original image signal detected from the stimulable phosphor sheets for picture elements at the other portions

A Predictor Switching Scheme for DPCM Coding of Video Signals

Abstract: In DPCM coding of video signals, for improved data compression efficiency, the predictor is often switched adaptively between two or more different predictions. For low-bit-rate coders, the predictor switching is done on a pel-by-pel basis. In this paper, a new scheme for predictor switching on a pel-by-pel basis is proposed. This new scheme is a modification of an existing adaptive predictor switching scheme which has been implemented in pel-recursive motion compensated coding of video signals. To evaluate the efficiency of the new scheme, a theoretical expression for the output bit rate is derived. It is pointed out under what conditions it is advantageous to use the new scheme for predictor switching. Some details of implementation are discussed. Results of computer simulation on natural scenes are presented. These results validate the theoretical conclusions derived in the paper. The simulation results also indicate that the picture quality is improved significantly, for approximately the same output bit rate, with the new predictor switching scheme as compared to the existing scheme for predictor switching.

Image forming method for dot matrix printer

Abstract: An image forming method for a color dot matrix printer prevents image quality from being deteriorated at the boundary between two nearby image areas which are developed by consecutive main scans. A paper is fed in a subscan direction by an amount which is one half of the width of a plurality of deflection steps, which is covered by one main scan, thereby developing an overlapping print area. The overlapping print area is subdivided at desired one of the deflection steps either column by column or color by color, an image segment in each of the resulting subregions being printed out by one of consecutive main scans.

Image design: Generation of a prescribed image through a diffraction-limited system with high-contrast recording

Abstract: Image restoration involves the recovery of an image which has been distorted by a given imaging system. "Image design," on the other hand, aims at determining the input image which when distorted by an imaging system (e.g., a display device) becomes a desired pattern. The image design problem is encountered in the design of masks for microphotography, microlithography, laser printing, and aids for the visually impaired. In this correspondence, we solve the "image design" problem using linear programming techniques for the case of an imaging system modeled by a band-limited linear system followed by a noninvertible point nonlinearity.

A Simplified EM Reconstruction Algorithm for TOFPET

Abstract: A simplified expectation-maximization (EM) algorithm for image reconstruction in positron emission tomography with time-of-flight information (TOFPET) has been developed. This new method requires substantially less computation time than the estimated posterior-density weighting (EPDW) method developed by Snyder and Politte [1,2]. Mathematically, the integration of TOFPET images at different angles yields a 2-D image which is the convolution of the true image and a rotationally symmetric point spread function (PSF). The new method uses this PSF to construct the probability functions and employs the summed TOFPET image as the incomplete data set in the expectation step of the EM algorithm; thus, the time-costly angle-by-angle operations required in EPDW are reduced to a single operation, cutting the processing time by a factor of approximately l/M for an image reconstruction using M projection angles. Results from computer simulation studies suggest that this new method may offer image quality superior to that produced by other algorithms.

Theoretical Bases And Measurement Of The Mtf For Integrated Image Sensors

Abstract: By analogy with optics, the spatial resolution of image sensors is generally characterized by the Modulation Transfer Function (MTF). This notion assumes the system being a linear filter, which is not the case in integrated image sensors, since they have a discrete photoelement structure. These sensors must in fact be considered as integral samplers. Their response to any irradiance distribution can thus be computed, knowing the pitch of photoelements and using a characteristic function. This function is more or less similar to the MTF. Once exact theoretical foundations have been defined, a computer simulation enables the various MTF measuring methods to be compared this makes it possible to rule out er-rors inherent to experiments. The most accurate and reliable method appears to be the knife edge method, applied with a relative displacement of the sensor and of the image. This avoids the occurence of aliasing phenomenon. Experimentation of this method for measurement of the CCD sensors characteristic function, which we call MTF as agreed, is described. This method also makes it possible to evaluate the transfer inefficiency of shift registers.

Objective assessment of mammography systems. Part I: Method.

Abstract: The authors have developed an experimental method for simultaneous determination of dose and image parameters in mammography. A global and objective quality concept, the image quality index, is proposed and its reliability demonstrated by tests of reproducibility. Objective quality tests and subjective evaluation by radiologists showed good correlation.

Picture signal transmission control system by encoding control at reception side

Abstract: PURPOSE: To select and watch an image favorite in picture quality at a preception side by controlling directly an encoding parameter related to an amplitude resolution, a spatial resolution, etc., with a request by the reception side that watches a sent image. CONSTITUTION: A favorite picture quality is instructed to a transmission equip ment from an image transmission equipments 10a or 10b at the reception side with picture quality instruction knobs 13a and 13b. In other words, an output according to the picture quality instructing knobs 13a and 13b rotated to the left or to the right is sent to an opposite side, and the equipment at the opposite side controls the encoding parameter according to the parameter. For example, when the picture quality instruction knobs 13a and 13b are turned in a left- handed direction, the encoding parameter is handled as an automatic control mode, and the automatic adjustment of the resolution is performed. On the other hand, when it is turned in a right-handed direction, a state is controlled so as to put the amplitude resolution and the spatial resolution at the minimum level, and a time base resolution becomes maximum relatively and the encoding of the image faithful to a motion can be performed. COPYRIGHT: (C)1987,JPO&Japio

Improved Tomographic Reconstruction in Seven-Pinhole Imaging

Abstract: Cardiac emission tomography using a seven-pinhole collimator has received only little appreciation as a diagnostic imaging technique. The main reasons are the limited angular sampling of the seven-pinhole device and the difficulties encountered in properly positioning the patient relative to the collimator/camera system. In order to overcome these problems, we have developed a modified ART3 algorithm for reconstruction of the radioactivity distribution in the heart. The method is very appropriate for seven-pinhole tomography, as demonstrated by the quality of the reconstructions, by the excellent point source resolution of the system response, and by a comparison to two other suitable reconstruction techniques, viz., SMART and SIRT.

Method and device for image formation

Abstract: PURPOSE:To obtain recording images of invariably high picture quality by forming a toner image on an image formation body while separating the image formation body and a transfer means from each other, and then forming a new toner image on said toner image, and transferring those toner images to a transfer material at a time after the image forming body and transfer means contacts each other. CONSTITUTION:A transfer roller 50 is brought into contact with the image formation body 1 through the operation of an eccentric cam 54, etc., after a toner image which is one color before a multi-color toner image is completed passes through a transfer position and right before the multicolor toner image is transferred, and rotates by being driven by the image formation body 1. Therefore, the transfer roller 50 neither damages a toner image nor is stained with toner, and the contamination of the reverse surface of the transfer material is evaded. Further, the transfer material which is fed while timed to transfer operation is entered into a transfer area smoothly by the transfer roller 50 which is already driven to rotate. Consequently, recording images of high picture quality are obtained with good transfer efficiency without the contamination of the back surface of the transfer material nor image shifting.