This research was conducted to achieve four objectives. The first objective was to develop an analytic model to predict the expected luminance distribution through the shadow mask structure on a color CRT display system. The model incorporates functions to describe the unique features of a color CRT, that is, the discrete sampling imposed by the shadow mask/ phosphor-dot arrangement as well as the electron beam phase relationships. The model also includes a flexible beam profile which allows the user to specify the desired shape of the beam profile, that is, whether the profile is described with a Gaussian, leptokurtic, or platykurtic distribution. This objective was fully satisfied with a computer program written in Lightspeed C which runs efficiently on Macintosh computers. The second objective was to determine detection thresholds for various levels of misconvergence of the three electron guns. When the three guns are properly registered, the luminance profiles converge and one perceives a color combination rather than the separate red, green, and blue luminances. Misconvergence is perceived by a change in the overall color or by color fringes, for example, a red edge to a yellow line. Past research has shown that threshold detection of misconvergence occurs when the primary beams are misconverged by 1 to 2 visual arcminutes of separation. This finding was replicated in this research for the two-color beam combinations which have previously been investigated, as well as for a white pixel, which involves all three guns. The third objective was to demonstrate the effect of misconvergence on the performance of a visual task and on subjective estimates of image quality. While subjective quality and threshold detection have previously been investigated for some color combinations, the three tasks (i.e., threshold detection, visual task performance, and subjective estimates) have not been systematically combined within the same data set for a variety of misconvergence conditions. This research provides such a composite data set. The subjective quality estimates were significantly correlated with the threshold detection data. In other words, as misconvergence of the display image increased, the probability of detection of misconvergence increased and the subjective quality rating decreased. However, the selected visual task (a short reading task with average reading time of 6.5 s) was not significantly affected by very large levels of misconvergence. Rather than conclude that the levels of misconvergence used in this research do not affect reading task performance, a more comprehensive visual task (e.g., a longer editing task, a random search task, or a map reading task) should be evaluated. The final objective was to evaluate the ability of selected image quality metrics which are computed from the model to predict threshold detection, subjective quality ratings, or visual task performance. The three metrics computed in this model (MTF Area, MTFA, and SQRI) are all based upon the modulation transfer function (MTF) of the display. These three computed metrics were for all practical purposes constant across the range of misconvergence. While this result was unexpected, it does suggest (1) that a model based only on luminance may be deficient because of the omission of chromaticity, and (2) that MTF-based metrics may not be an appropriate representation because misconvergence does not change the display’s ability to transmit information, but is a phase shift along the shadow mask. As summarized, this research successfully met three of the stated objectives. Further, it points toward future research opportunities to further this type of modelling effort and to successfully develop image quality metrics for color displays. / Ph. D.

A study was conducted to investigate the effects of color CRT misconvergence and display luminance on reading performance and perceived image quality. The objectives of this study were (1) to determine the effects of color CRT misconvergence on reading time and errors, (2) to determine the effects of color CRT misconvergence on subjective ratings of image quality, and (3) to examine the interaction between color CRT misconvergence and display luminance upon reading performance and subjective ratings of image quality. Ten participants performed a Tinker Speed of Reading Test on a shadow-mask, color CRT computer workstation. Both search time to find the out-of-context word and errors were recorded. Following the reading task, each participant rated the image quality of the display using a 9-point subjective scale. Reading performance was not affected by CRT misconvergence or character luminance. Increasing misconvergence did result in lower image quality ratings; however, it was found that participants perceived the more luminous displays to have higher image quality. Also, it was determined that image quality ratings were lowest for magenta misconvergence. However, using normalized ratings, it was found that image quality ratings decreased quickest for the yellow characters with increasing misconvergence. These findings indicate that lower levels of misconvergence (1 to 2.5 arcmin) may not affect reading performance adversely. However, since individuals perceive display quality to be poor at these levels of misconvergence, color CRTs should be used only when application absolutely requires them. / Master of Science

Our information-oriented society relies on the widespread use of color CRT displays. Misconvergence of the primary colors of a shadow-mask CRT is a problem with this technology that deserves human factors engineering consideration. The purpose of this research was as follows: (1) to determine the effects of misconvergence type and amount and font type on reading performance (time required and errors made), (2) to determine the effects of misconvergence type and amount and font type on subjective image quality ratings, (3) to determine the role of luminance and chrominance contrasts in predicting performance or subjective ratings. Ten participants performed a simple reading task and rated the image quality of the text they had just seen using a nine-point scale. The text was presented on a shadow-mask CRT. Different misconvergence types and amounts and different font types were presented. Neither font type, misconvergence type, nor misconvergence amount affected the time required to perform the reading task. Only misconvergence type affected the rate at which errors occurred, with blue misconvergence of a white character resulting in the most errors and cyan misconvergence resulting in the fewest errors. Font type, misconvergence type, misconvergence amount, and the misconvergence type and amount interaction all affected subjective ratings, with 1 to 2 arcmin being the largest acceptable misconvergence amounts. The Yu'v’ chrominance contrast between the stationary misconvergence fringe and the background was positively correlated with subjective preference ratings. / Master of Science

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Thesis (Ph. D.)--University of California, San Diego, 2003. / Vita. Includes bibliographical references (leaves 371-389).

An introduction to the fundamental concepts of X-ray physics and X-ray tube design is given. This discussion also includes a brief description of various X-ray tube types available commercially for a number of different industrial applications. The design of a high-energy MgO cold cathode X-ray tube, which is to be used in an X-ray fluorescence (XRF) spectrometer, is described in detail with emphasis placed on the electron beam focusing mechanism and the theory of operation as well as the construction of the X-ray tube MgO cold cathode, which functioned as the electron emitter of the device. A detailed account is also given of the output characteristics of the X-ray tube power supply, which has a direct effect on the design requirements and consequently the performance of the X-ray tube. An investigation into the manufacture of the vacuum envelope with particular attention focused on the production of reliable metal-to-ceramic seals was performed. A number of tests were conducted especially with regard to the maximum temperature that such seals may withstand without becoming permanently damaged. These tests were essential, since high temperature gradients tend to develop in an X-ray tube during operation, which the metal-to-cerarnic seals of the tube must be capable of withstanding if damage to the device is to be avoided. The set-up of the XRF spectrometer in which the completed X-ray tube was tested is discussed, in which the X-ray current and voltage measuring techniques are described. Furthermore a detailed account of the operation of the X-ray detector system and the multichannel analyser is given, which was used to detect and record spectra of the sample elements excited by the primary radiation of the X-ray tube. Finally the measured X-ray tube performance characteristics are discussed and compared to the predicted results. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

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Made available in DSpace on 2014-10-09T12:35:12Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:40Z (GMT). No. of bitstreams: 0 / A motivação deste trabalho foi o desenvolvimento e validação de um dispositivo para realizar os testes estabelecidos na ABNT NBR IEC 60601-1-3 nas versões publicadas de 2001[1] e 2011[2]. A finalidade dos ensaios é determinar a camada semirredutora - CSR (Half Value Layer - HVL) e a filtração com equivalência de qualidade, em mmAl, dos materiais que interceptam o feixe de raios X desde a sua emissão até o dispositivo receptor de imagem de raios X. Esta filtração inclui os materiais presentes no conjunto fonte de radiação X, formado pela cúpula de proteção radiológica com o tubo de raios X inserido, pelo sistema de colimação (filtração inerente) e pelos materiais presentes nos suportes de pacientes, como mesa e bucky mural sendo que ambos incorporam dispositivo receptor de imagem que também é avaliado. No desenvolvimento foi levada em consideração a rotina da execução do ensaio, com a finalidade de diminuir ao máximo a interação do operador com o sistema, a fim de reduzir o fator humano na execução, refletindo diretamente na incerteza de medição, na diminuição do tempo de execução e na segurança radiológica. O dispositivo desenvolvido foi validado com relação aos seguintes aspectos: a) Influência do dispositivo trocador de filtros quanto ao posicionamento e distribuição dos filtros; b) Influência da pureza dos filtros de alumínio utilizados no dispositivo, e a c) Comparação entre os ensaios realizados com dispositivo de ensaio desenvolvido com relação aos ensaios realizados com um gerador de raios X de referência. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP