Harry L. Snyder

The sensitivity of response measures of alphanumeric legibility to variations in dot matrix display parameters.

This research evaluated the sensitivity of four observer response measures to variations in the character size and dot luminance of a dot matrix display. Specifically, the research determined the sensitivity of recognition accuracy, response time, tachistoscopic recognition accuracy, and threshold visibility. Alphanumeric characters were presented to six subjects in noncontextual form on a variable-parameter CRT display programmed and driven by a minicomputer. Recognition accuracy (percent correct response) was found to be the response measure that is most sensitive to the display parameters of character size and dot luminance. Character size, dot luminance, and viewing distance proved to have consistent and significant effects at viewing distances greater than 1.52 m. At lesser viewing distances, these parameters had little effect. The results suggest that there is no major difference between the display requirements for computer-generated dot matrix displays versus those for conventional CRT displays.

Comparison of depth cues for relative depth judgments

This paper reports on two experiments in which subjects judged the relative depth ordering and subjective quality of depth of simple, geometric figures (planar circle, square, and triangle). The 3-D images were presented on a Tektronix SGS 620 field-sequential stereoscopic CRT. Four sources of depth information (cue types) were combined factorially to construct exemplary 3-D images: Relative Size (angular subtense decreased with increasing depth); Disparity (binocular disparity varied from crossed to uncrossed with increasing depth); Interposition (closer figures overlapped ones farther away in depth); and Luminance (luminance decreased with increasing depth). Inclusion of each of the three monocular cues produced significantly faster depth judgments. However, there was a lack of significant response time effects associated with binocular disparity. Conversely, stereo presentations strongly improved ratings of subjective image quality. These data indicate that stereoscopic images may provide subjectively more compelling depth information than images containing only monocular cues. However, they also provide evidence for at least one limitation of stereoscopic display utility.

Imaging quality determines differences in reading performance and perceived image quality with CRT and hard-copy displays

The effects of physical image quality on reading and on perceived image quality from CRT and hard copy displays (photographs) were studied. The results showed that as the image quality of a display increased, indicated by an increase in the value of the modulation transfer function area (MTFA), the reading speed and subjective image quality ratings increased. This change in reading speed and perceived image quality occurred similarly for both hard-copy and soft-copy conditions. If the image qualities of the displayed text are similar, hard-copy and softcopy displays will yield equivalent reading speeds.

Braking Movement Time and Accelerator-Brake Separation

Movement times were obtained for nine adult drivers for three accelerator-brake pedal separations. The typical separation (6.35 cm laterally and 5.08 cm vertically) produced significantly longer movement times than did either a 10.16-cm or 15.24-cm lateral separation with no vertical separation.

Effect of Image Polarity on VDT Task Performance

Three experiments were conducted in which positive and negative contrast on visual display terminals were directly compared. Operator tasks included visual search and reading, with accuracy and timeliness of response measured. In all cases where significant differences exist, better performance was obtained with negative contrast (dark characters or symbols on a lighter background). The increases in performance range from a low of 2.0 percent to a high of 31.6 percent. Based on the above results, we believe that there are significant advantages in visual task performance obtained from the selection of negative contrast displays. Current standards that require negative contrast appear to be justified, while future revisions of ANSI/HFS 100-1988 and other standards should seriously consider incorporating negative contrast as a recommendation or requirement.

Image Quality: Measures and Visual Performance

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.

Chapter 20 – Image Quality

Publisher Summary This chapter discusses image quality. It focuses on the physical nature of the display and ways in which it can be made more compatible with both the human user and the environment in which it is placed. The advent of commercial television, the application of commercial television technology to computer-system displays, and the development of flat-panel displays have done a lot to force the development of image quality measurement techniques. At the same time, only a small number of laboratories and facilities in the United States have the capabilities to make the image quality measurements on a variety of display surfaces. Even those laboratories have some minor disagreement as to the appropriate techniques for measuring certain characteristics of the displays. Moreover, there is some disagreement as to the best image quality metric to be applied to visual displays in general. Nonetheless, a variety of image quality measurements have been made and evaluated in recent years, with a general agreement among display engineers and visual scientists that modulation transfer function-based measures are appropriate and empirically useful.

Keyboard Design: An Investigation of User Preference and Performance

This study investigated the effects of several alphanumeric keyboard characteristics including: audible feedback; location, size, and shape of the carriage return key; and the shape and style of keycaps. Four of the six keyboards were experimental prototypes, while the remaining two were production models. Eighteen subjects were used in a mixed factorial design. Subjects performed a text entry task during which they were not allowed to correct any errors. Four types of data were collected: 1) total errors per trial, 2) total time for text entry, 3) individual preference questionnaire data for each keyboard, and 4) comparative questionnaire data across keyboards. Results indicate that time on task was not significantly different among keyboards; however, with audible feedback, a marginally significant result was found. Highly trained typists committed significantly more errors than did the other two less experienced groups. Subjects indicated that the location, size, and shape of the return key were important factors for keyboard design. Across groups, subjects preferred the capability for audible feedback.

Image Quality and Face Recognition on a Television Display

Subjects were asked to match faces presented singly on a television display with one of 35 faces presented on a photographic display. The probability of correct recognition and the time required to recognize the single face were related to the quality of the television image. Image quality was varied by changing the square-wave response of the television system and the video signal-to-noise voltage ratio. A derived unitary metric of image quality, the square-wave modulation transfer function area, MTFASQ, was shown to correlate highly with both measures of observer performance. The utility of this metric for systems design is discussed.

Color Contrast Metrics for Head-up Displays

Recent evidence suggests that a useful metric of color contrast can be formulated in terms of distance between colors in a perceptually uniform color space. The present research adds to this evidence by presenting equations which relate distance in several spaces to response speeds for reading colored numerals superimposed upon colored backgrounds. The results suggest that several extant uniform color spaces provide no definite advantages over the (nonuniform) 1931 CIE tristimulus space and that improvements can be obtained by rescaling their axes. Two computationally simple metrics are presented which model global color contrast and color contrast complexity.