Contrast (vision)

About: Contrast (vision) is a research topic. Over the lifetime, 10379 publications have been published within this topic receiving 221480 citations.

Effect of a cataract simulation on clinical and real world vision.

Abstract: AIMS/BACKGROUND: Many reports have indicated that some patients with cataract can retain good visual acuity but complain of significant visual problems. This is the first in a series of papers trying to determine what causes these symptoms and whether other clinical tests can predict the real world vision loss. METHODS: The effect of a cataract simulation with a similar angular distribution of light scatter as real cataract on clinical (visual acuity, contrast sensitivity, and disability glare) and real world vision (face recognition, reading speed, and mobility orientation) was investigated. RESULTS: The simulation had a relatively small effect on visual acuity (6/6 with the simulation), but much larger effects on contrast sensitivity and low contrast acuity with and without glare. The simulation had no effect on high luminance and high contrast real world tasks, such as mobility orientation in room light and optimal reading speed. A small, but significant deterioration was found for the slightly lower contrast task of face and expression recognition. However, under low luminance conditions, substantial defects in mobility orientation were obtained (despite 6/6 acuity). CONCLUSIONS: Although the relative effect of the cataract simulation on acuity and contrast tasks is not typical of the average cataract, it can be found in those cataract patients with visual problems despite good visual acuity. This corroborates the suggestion that it is large amounts of wide angle light scatter (forward and/or backward) which are at least partly responsible for visual disability in cataract patients with good visual acuity. A patient's reported visual disability may depend on the percentage of time he or she spends under low contrast and/or low luminance conditions, such as walking or reading in dim illumination, and walking or driving at night, in fog, or heavy rain.

The influence of age on the spatial and temporal contrast sensitivity function.

Abstract: A clinical technique for sampling the spatial and temporal CSF at low, intermediate and high frequencies is described. Reductions in contrast sensitivity with age were shown with the highest spatial and temporal frequency stimuli. The reductions can be almost completely accounted for by the reduction of pupil area with age, causing a reduction in retinal illuminance. The results show a significant deterioration in vision with age that is not revealed by standard visual acuity testing.

Envelope-responsive neurons in areas 17 and 18 of cat.

Abstract: 1. Single cortical neurons are known to respond to visual stimuli containing Fourier components only in a narrow range of spatial frequencies. This investigation demonstrates that some neurons in cat area 17 and 18 can also respond to certain stimuli that have no Fourier components inside the cell's luminance spatial frequency passband. 2. To study such “non-Fourier” responses, we used envelope stimuli that consisted of a high-spatial-frequency sinusoidal luminance grating (carrier) whose contrast was modulated by a low-spatial frequency sine wave (envelope). There was no Fourier component at the apparent periodicity of the envelope spatial frequency. However, some cells responded to such a “phantom” component of the envelope modulation when it fell inside the cell's luminance spatial frequency passband while all the real Fourier components in the stimuli were outside. 3. We conducted extensive control experiments to eliminate the possibility of producing artifactual responses to the envelope stimuli due to any small residual nonlinearity of the z-linearized CRT screen. The control experiments included 1) testing of screen linearity to ensure that the effect from the residual screen nonlinearity was no larger than the sensitivity level of visual responses and 2) comparing the responses to envelope stimuli with the responses to the equivalent contrast of the artifact produced by the screen nonlinearity. All these control experiments indicated that any effect of screen nonlinearity did not contribute significantly to the neural envelope responses. 4. We performed a statistical analysis to obtain an index of relative strength of envelope responses for each cell and to objectively classify cells as “envelope-responsive” or “non-envelope-responsive.”(ABSTRACT TRUNCATED AT 250 WORDS)

Method and system for automatic brightness and contrast adjustment of a video source

Abstract: An image brightness and contrast management module for automatically adjusting brightness and contrast of an input video signal includes a histogram generation unit that generates a pixel luminance histogram based on pixel luminance values in a frame, whereby the histogram shows a distribution of luminance values in the frame and indicates the dynamic range and the dominant luminance value(s) for the frame. The module includes a histogram characterization unit that uses the pixel luminance histogram to identify which of a plurality of brightness/contrast properties is exhibited in the frame. The module also includes a brightness and contrast adjustment unit that nonlinearly adjusts, in real-time, the pixel luminance values in a next frame based on the identified brightness/contrast properties exhibited in the preceding frame. In this manner, bright or dark dominant areas of an image are stretched to enhance the contrast of the dominant luminance values without blackening the darker portions or saturating the brighter portions of the image.