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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Color discrimination of small targets /

Highnote, Susan M. January 2003 (has links)
Thesis (Ph. D.)--University of California, San Diego, 2003. / Vita. Includes bibliographical references (leaves 371-389).
22

A human spatial-chromatic vision model for evaluating electronic displays

Lloyd, Charles J. C. 19 October 2005 (has links)
This dissertation examines those attributes of full-color display systems (particularly color matrix displays) which degrade image quality. Based on this analysis, it is suggested that a comprehensive metric should measure image quality in terms of transmitted signal and noise modulation, both achromatic and chromatic. Moreover, it is suggested that these signal and noise measurements be weighted in terms of human spatial-chromatic visual characteristics. A review of extant image quality metrics reveals several limitations of these metrics which make them unsuitable for the evaluation of color matrix displays. These limitations include the inability to account for chromatic modulation transfer and chromatic noise as well as the general inability to account for spatial and grey-scale sampling. This work describes a new methodology for assessing image quality that can be applied to full-color as well as monochromatic, and sampled as well as continuous, display systems. Unlike most display quality metrics, the proposed methodology is not based on the tools of linear systems analysis. Rather, it is based on more veridical models of the human visual system (HVS), including multi-channel models of spatial vision, the zone theory of color vision, physiological models of retinal processes, and models of the optics of the eye. A display evaluation system consisting of the HVS model used in conjunction with a display simulator is described. The HVS model employs nine image processing stages to account for nonlinear retinal processes, opponent color encoding, and multiple spatial frequency channels. A detailed procedure for using the HVS model to evaluate display systems is provided. The validity of the HVS model was tested by conducting contrast detection, discrimination, and magnitude estimation experiments on the model. The results of these experiments correspond closely with published human performance data The utility of the display evaluation system was assessed by making image quality predictions for the display systems used in three image quality studies. Image quality predictions using the proposed system correlate strongly with ratings of image quality provided by human subjects. Results of these validation studies indicate that the proposed method of display evaluation is viable and warrants further development. / Ph. D.
23

Effects of depth cues on depth judgements using a field-sequential stereoscopic CRT display

Reinhart, William Frank 13 July 2007 (has links)
Current interest in three-dimensional (3-D) information displays has focused on the use of field-sequential CRT techniques to present binocular stereoscopic images. Although it is widely believed that stereopsis provides a potent depth information cue, numerous monocular cues exist which may augment, detract from, or even supplant stereopsis. Unfortunately, few guidelines or well-controlled analyses on the use of depth cues are available to direct engineering implementations of stereoscopic display systems. This dissertation describes three experiments using 3-D images presented on a Tektronix SGS 620 field-sequential stereoscopic CRT (19-inch diagonal, 120-Hz field rate, passive glasses). In the first experiment, 10 participants with normal vision judged the relative apparent depth ordering of three simple geometric figures (planar circle, square, and triangle). Four sources of depth information (cue types) were factorially combined to construct exemplary images of planar figures in apparent depth: Relative Size (angular subtense decreased with increasing apparent depth); Disparity (binocular disparity varied from crossed to uncrossed with increasing apparent depth); Interposition (closer figures partially occluded ones farther away in apparent depth); and Luminance (luminance decreased with increasing apparent depth). The three monocular cues (Interposition, Size, and Luminance) produced significantly faster depth judgments when used alone; however, when used in combination, Interposition dominated the response time data trends. Although the Disparity cue received moderately high "perceived effectiveness" ratings, response time measures indicated that it played a minor role in the relative depth judgment task. The second experiment was conducted to investigate further the subjective value of the various depth cues. Participants rated subjective image quality (quality of depth) rather than making rapid relative depth judgements. As anticipated, the most satisfactory ratings of depth were made for display images which included stereoscopic depth (Disparity), with the very highest ratings given to display images which included all four depth cues. The results of these first two experiments illustrated a task-demand (objective vs. subjective) discrepancy in the utility of stereoscopic depth cues. The third experiment extended the initial work to include more geometrically complex stimuli in visual search and cursor positioning tasks. In these task environments, stereoscopic disparity and monocular depth cues had an interactive effect on improving visual search times and reducing cursor positioning errors on the depth axis, with the best performance associated with the presence of all depth cues. The complementary nature of these effects was attenuated when depth cue salience was elevated to suprathreshold levels. Based on the results of this research, recommendations are presented for the display of depth information with the stereoscopic CRT. The importance of this research is underscored by the fact that while technological advances have been made in the field of stereoscopic display, very few usability data exist either from laboratory testing or from the implementation of such displays in operational systems. This research provides information to complete cost/performance benefit analyses for 3-D display designs which could in turn significantly impact industry acceptance of the field-sequential stereoscopic CRT. / Ph. D.
24

The effects of image quality on reading performance and perceived image quality from CRT and hard-copy displays

Jorna, Gerard C. 07 February 2013 (has links)
The effects of physical image quality on reading and on perceived image quality from CRT and hard copy were studied in this experiment. The results showed that as the image quality of a display increased, indicated by an increase in the value of the MTFA, the reading speed increased and subjective image quality V; ratings increased. This change in reading speed and perceived image quality occurred in the hard copy as well as in the soft copy condition. Image quality, therefore, is concluded to be the major determinant of subjects' performance with respect to displayed information. This implies that if the image quality the displayed text ls the same on the display techniques used, subjects will read from CRT displays as fast as from hard copy displays. / Master of Science
25

Unitary suprathreshold color-difference metrics of legibility for CRT raster imagery

Lippert, Thomas M. January 1985 (has links)
This dissertation examined the relationships between color contrast and legibility for digital raster video imagery. CIE colorimetric components were combined into three-dimensional color coordinate systems whose coordinates map one-to-one with the physical energy parameters of all colors. The distance between any two colors' coordinates in these 3-spaces is termed Color-Difference (ΔE). ΔE was hypothesized as a metric of the speed (RS) with which observers possessing normal vision could accurately read random numeral strings of one color displayed against backgrounds of another color. Two studies totaling 32064 practice and experimental trials were conducted. The first study determined that the CIE Uniform Color Spaces are inappropriate for the modeling of RS. Subsequently, a different 3-space geometry and colorimetric component scaling were empirically derived from the Study 1 data to produce a one-dimensional ΔE scale which ” approximates an interval scale of RS. This ΔE scale and others were then applied to the different stimulus conditions in Study 2 to determine the generalizability of such ΔE metrics. The pair of studies is conclusive: several ΔE scales exist which serve equally well to describe or prescribe RS with multicolor CRT raster imagery for a range of character luminances in both positive and negative presentation polarities. These are the Y,u',v', logY,u',v', L*,u',v', and L*,u*,v* rescaled color spaces. Because of its predictive accuracy and simplicity, a luminance—generalized, ΔE—standardized Y,u',v' metric, accounting for 71% and 75% of the RS variability in Studies 1 and 2, respectively, is recommended as the most appropriate metric of emissive display legibility to be tested in these studies. / Ph. D.
26

Effects of Discharge Tube Geometry on Plasma Ion Oscillations

Simmons, David Warren 05 1900 (has links)
This study considers the effect, on plasma ion oscillations, of various lengths of discharge tubes as well as various cross sections of discharge tubes. Four different gases were used in generating the plasma. Gas pressure and discharge voltage and current were varied to obtain a large number of signals. A historical survey is given to familiarize the reader with the field. The experimental equipment and procedure used in obtaining data is given. An analysis of the data obtained is presented along with possible explanations for the observed phenomena. Suggestions for future study are made.

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