Aspects Of Image Quality Research Articles

Standardization of Perceptually Based Image Quality for Printing Systems (ISO/IEC JTC1 SC28 and INCITS W1.1)

With the single exception of ISO 13660, there are no generally accepted international standards for describing the image quality of printing systems. ISO 13660 provides simple guidelines for the quantitative measurement of many aspects of image quality for binary, monochrome, printing systems, and has had a significant impact in the printing industry. However, as in most measures of imaging system performance, the visual significance of a measurement difference is not addressed in ISO 13660. This weakness prevents a truly meaningful comparison of printing system specifications. To address this weakness, and to provide evaluation methods applicable to more capable systems incorporating gray-level and full-color imaging technologies, INCITS W1, the U.S. representative of ISO/IEC JTC1/SC28, has been chartered to develop an appearance-based image quality standard. This paper will describe the objectives, the development process, the current status, and the results achieved so far by the many contributors to the development of this standard.

Scanning Image System for Print Quality Measurements

Printronix, Inc. uses scanner-based image systems to perform print quality measurements for line-matrix printers. The size of the image samples and image definitions requirement make commercial scanners convenient to use. The scanner-based image quality measurement system has been utilized to increase repeatability and accuracy. Printronix has developed software package, based upon MATLAB, which permits the use of standardized algorithms to interpret the data. The PC based analysis tool can process data efficiently and yield more accurate results. Additionally, the new method can provide in-depth information on individual attributes that contribute to the overall visual perception of image quality. This paper presents the measurement and analysis methods of determining the quality of prints generated by line matrix printers. Several key image quality aspects such as dot density, dot size, dot uniformity, dot positioning, and ink smearing measurement, are discussed in the paper.

Equipment Requirements and Specification for Digital and Interventional Radiology

During the past decade there has been a substantial growth in digital and interventional radiology. Equipment requirements and specification for digital (interventional) radiology are necessary to facilitate the purchase of proper installations for specific purposes. Inappropriate equipment might lead to increased dose to patients and staff, insufficient image quality and, for interventional radiology, to inefficient procedures and the potential for deterministic effects to occur. The equipment requirements and specifications are of various types. Requirements for dose displays and dose record keeping are dealt with in a separate contribution to this workshop. Detailed information is presented in this contribution on requirements and specifications in relation to ergonomic, dosimetric and image quality aspects.

Image quality assessment and radiation doses in intraoral radiography

Objective: The purpose of this study was to investigate 2 very important aspects of dental radiographic image quality, exposure time settings and film processing, and to assess their relation to radiation dose. Study Design: Radiographic images of a dental image quality test tool were obtained in 108 dental practices. Image quality and film processing were evaluated both subjectively and objectively by comparing films developed by the dentists with films developed under optimum conditions. The data consisted of measured values of optical density, which were used to obtain image contrast, and scores of image quality and film processing, which were based on criteria set by 2 independent oral radiologists. Entrance surface dose was also measured for the technique used at each dental practice. Results: The results indicate a great variability of exposure time settings used by the dentists for imaging the phantom. Film processing was inadequate in most of the practices, which resulted in poor image quality and increased patient radiation doses. The mean entrance surface dose for imaging the phantom was 3.8 mGy. Conclusion: Intraoral imaging techniques and film processing must be standardized to improve image quality and further reduce patient radiation doses. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91:362-8)

Characterization of color CRT display systems for monochrome applications.

Soft-copy presentation of medical images is becoming more and more important as medical imaging is strongly moving toward digital technology, and health care facilities are converting to filmless hospital and radiological information management. Although most medical images are monochrome, frequently they are displayed on color CRTs, particularly if general-purpose workstations or PCs are used for medical viewing. In the present report, general measurement and modeling procedures for the characterization of color CRT monitors for monochrome presentation are introduced. The contributions from the three color channels (red, green, and blue) are weighted according to the spectral sensitivity of the human eye for photopic viewing. The luminance behavior and the resolution capabilities of color CRT monitors are analyzed with the help of photometer and charge-coupled device (CCD) camera measurements. For the evaluation of spatial resolution, a two-dimensional Fourier analysis of special test images containing white noise (broadband response) is employed. A stage model for a color CRT monitor is developed to discuss the effects of scanning and dot sampling. Furthermore, display intrinsic veiling glare and reflectivity of typical color CRT monitors are measured and compared with those of monochrome CRT monitors. The developed methods and models allow one to describe the image quality aspects of color monitors if they are applied for medical monochrome image presentation. Particularly, because of the reduced luminance and dynamic range of color monitors, the calibration and control of their luminance curves is a very important task. For present color CRT monitors, 1,280 x 1,024 turns out to be an intrinsic limit for the displayable matrix of medical images.

RADARSAT image quality and calibration — Update

This paper reviews image quality and radiometric calibration aspects of the first two years of operation of RADARSAT. This includes the calibration of almost all beams (a total of more than 25 beams when considering shifted positions of each of the Fine beams), and the stability and calibration accuracies achieved during the mission to date. The measurements show that the SAR performance is better than the specifications. In September 1997, RADARSAT underwent a major configuration change to accommodate the Antarctic Mapping Mission for a period of about five weeks. To achieve this, the spacecraft was rotated to allow imaging from a left-looking geometry. The image quality and calibration results for the left-looking mode are also discussed.

An Engineering Approach to Consistent Images: Control of Video and Film Image Quality in TV Production

Engineers, video operators, colorists, and producers all share the goal of excellence in television image quality. This paper explores the reasons why some popular and widely used techniques to standardize video and film quality have met with mixed success, and a practicable solution is proposed. Previous efforts have, by and large, lacked the precision to ensure consistent high-quality images, particularly in regard to tonal range and color. The system under discussion, although providing production teams with infinite freedom for artistic expression, controls the technical aspects of image quality from camera setup through the post-production process.

Amorphous Semiconductors Usher in Digital X-Ray Imaging

Unlike other major medical imaging methods, such as computed tomography, ultrasound, nuclear medicine and magnetic resonance imaging—all of which are digital—conventional x-ray imaging remains a largely analog technology. Making the transition from analog to digital could bring several advantages to x-ray imaging: Contrast and other aspects of image quality could be improved by means of image processing; radiological images could be compared more easily with those obtained from other imaging modalities; the electronic distribution of images within hospitals would make remote access and archiving possible; highly qualified personnel could service remote or poorly populated regions from a central facility by means of “teleradiology”; and radiologists could use computers more effectively to help with diagnosis—work that has already been initiated at the University of Chicago by Kunio Doi and his coworkers.

Volumetric object reconstruction using the 3D-MRF model-based segmentation.

A number of segmentation algorithms have been developed, but those algorithms are not effective on volume reconstruction because they are limited to operating only on two-dimensional (2-D) images. In this paper, we propose the volumetric object reconstruction method using the three-dimensional Markov random field (3D-MRF) model-based segmentation. The 3D-MRF model is known to be one of efficient ways to model spatial contextual information. The method is compared with the 2-D region growing scheme under three types of interpolation. The results show that the proposed method is better in the aspect of image quality than other methods.

Grundlagen der Spiral-CT: I. Prinzipien von Aufnahme und Bildrekonstruktion

The principles of Spiral-CT, all aspects of image quality and consequences derived for constancy tests and other quality assuring measures as well as considerations on dose are presented in a series of four articles. In part I, the principles of data acquisition and image reconstruction are discussed in detail. Spiral-CT represents the first scan mode in non-planar geometry which was successfully implemented in CT. The basis for this achievement has been the development of various algorithms for z-interpolation, an additional preprocessing step to calculate planar data sets for arbitrary table positions from the spiral data set. Images are reconstructed from these data sets by the usual process of convolution and backprojection. The z-interpolation algorithms currently in use will be described and additional approaches which are currently only rarely used are explained. Details on image quality will be discussed in part II, aspects of image quality measurements and quality assurance in part III, and considerations on dose in part IV.

Calibration and image quality performance results of RADARSAT

The Canadian earth observation satellite, RADARSAT, was launched in late 1995. The aim of this space borne Synthetic Aperture Radar (SAR) program is to provide C-band HH polarized SAR data products for five years at varying incidence angles, resolutions and area coverages. The system has been designed to produce imagery using single beams in elevation and also to operate in the ScanSAR mode by combining different elevation beams. SAR images have been obtained and were used to measure system performance during the Beam Qualification Phase. The measured image quality parameters for single beam products dealing with all aspects of image quality except radiometric calibration have been found to meet and exceed the system specifications. Based on the system performance and on completion of the commissioning activities, the Initial Operational Capability for the system was declared in April 1996.

Instrument- and computer-related problems and artifacts in nuclear medicine

Advances in gamma-camera design over the last 5 to 10 years have improved all aspects of image quality, particularly for tomographic imaging. As system complexity increases, it becomes more important that both the technologist and physician be able to recognize the various types of artifacts that can occur in gamma-camera systems and their potential impact on clinical studies. A thorough evaluation of the system at installation and a comprehensive quality control program will detect most problems that can occur. The most sensitive indicator of gamma-camera performance is uniformity. Because this measurement is performed on a daily basis, it is the principle tool in evaluating the status of the gamma-camera. Most artifacts related to the integrity of the detector head, computer system, and hard copy device can be detected on the uniformity image. For tomographic imaging, a quantitative determination of uniformity is needed to ensure that the system will not introduce ring artifacts into the patient data. Unlike planar imaging, the complex nature of tomographic imaging requires additional checks on system performance to ensure that other components of the system, such as the collimator, gantry, and imaging table, are not a source of artifact in the reconstructed image data. Failure of a system component can occur at any time and may be subtle and difficult to recognize in modern systems. In such an environment it becomes imperative that any unexpected finding in a clinical study be questioned with respect to a possible malfunction of some aspect of data acquisition and analysis.

The perception and measurement of contrast: the influence of gaps between display elements

Abstract The influence of the luminance of the gap between display elements of flat panel displays (FPDs) on perceived contrast was investigated. Twelve black-on-white FPDs, differing systematically with respect to foreground, background, and gap luminance, were simulated in an experiment. Twelve subjects rated each simulation on u scale, measuring several aspects of image quality, and performed a search task with each simulated FPD. The aims of the research were (a) to validate and assess the reliability of the rating scale items concerning contrast; (b) to relate subjective to objective measures; (c) to find out if ratings improve if raters perform a task with the rated objects; and (d) to evaluate a metric for expressing FPD contrast that we recently proposed. It is concluded that (a) the scale items are reliable if the rated objects vary on the property under concern; several items consistently measured subjective contrast; (b) subjective and objective contrast were strongly related in a linear fashio...

Image Quality and Dosimetric Aspects of Chest X Ray Examinations: Measurements with Various Types of Phantoms

Image Quality and Dosimetric Aspects of Chest X Ray Examinations: Measurements with Various Types of Phantoms

Image Quality and Dosimetric Aspects of Chest X Ray Examinations: Measurements with Various Types of Phantoms

Image Quality and Dosimetric Aspects of Chest X Ray Examinations: Measurements with Various Types of Phantoms

A study of the relationship between routine ultrasound quality assurance parameters and subjective operator image assessment.

Comparisons have been made between a number of routine quality assurance (QA) measurements and a number of related subjective aspects of image quality. These comparisons between lateral resolution and perceived definition, dynamic range and subjective grey-level assessment, and slice thickness and overall image quality appraisal showed very poor correlation. We deduce from this that other QA parameters are needed to quantify good image quality as defined by the operators.

Clinical utility of high-resolution portal films

We have evaluated the film quality and overall clinical utility of a unique high-resolution portal film system which utilizes high contrast graphics art film. A total of 127 unselected patients had their conventional portal films and high-resolution films of the same site, compared and graded subjectively for a variety of parameters by an independent panel of radiotherapists and radiographers. Although consistent improvements in most aspects of image quality were noted, improved overall clinical usefulness of the high-resolution portal film system in comparison to the conventional films, when subjected to multiple regression analysis, was confined to lateral neck views only. High-resolution portal film utility was also found to depend significantly on field size with areas less than 110 cm 2 having a markedly worse clinical utility score.

Book reviewsICRU Report 41. Modulation Transfer Function of Screen-Film Systems. ICRU, pp. vi + 56, 1986 (NCRP/ICRU, Bethesda, USA), $16.00. ISBN 0–913394–35–1

This publication describes the concepts used in the analysis of the physical aspects of radiographic image quality. It provides information about the significance and quantification of radiographic noise and contrast and describes transfer functions that can be used to quantify the resolution properties of imaging systems and their component parts. There are sections on image quality, transfer function analysis, the measurement of modulation transfer function (MTF) and a section which describes factors affecting the MTFs of radiographic screen-film systems. The transfer function analysis is based principally on published articles by Rossman (1969, Radiology, 93, 257): this includes descriptions of linearity, shift invariance, point spread function, line spread function (LSF), convolution, MTF and the Fourier spectrum. Although the main text is void of mathematics, there is an appendix in which there are mathematical derivations of the principal functions. There is also a useful glossary where important technical terms are defined, and excellent bibliography and reference sections.

Adaptive Transform Coding And Image Quality

A review of adaptive image transform coding techniques is given. Adaptive techniques are superior to nonadaptive procedures; however, their implementation requires a significant degree of added complexity. A major aspect of adaptive transform coding is the understanding and utilization of the local statistical structure of the image. Rate adaptive communication and buffer feedback are also important aspects of adaptive coding procedures. The discussion emphasizes the image quality aspect of the coding process.

The Use of Models for Optimizing Image Quality

AbstractComputer optimization of any system implies that its relevant properties can be expressed in terms of the same set of basic variables.Existing models describing various aspects of image quality are discussed from this standpoint.It appears that the above condition is not generally met.