Contrast (vision)

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

Colour Retinal Image Enhancement Based on Domain Knowledge

Abstract: Retinal images are widely used to manually or automatically detect and diagnose many diseases Due to the complex imaging setup, there is a large luminosity and contrast variability within and across images Here, we use the knowledge of the imaging geometry and propose an enhancement method for colour retinal images, with a focus on contrast improvement with no introduction of artifacts The method uses non-uniform sampling to estimate the degradation and derive a correction factor from a single plane We also propose a scheme for applying the derived correction factor to enhance all the colour planes of a given image The proposed enhancement method has been tested on a publicly available dataset Results show marked improvement over existing methods

High and low contrast acuity and clinical contrast sensitivity tested in a normal population.

Abstract: Visual acuities obtained with a high contrast Bailey-Lovie chart (HCBL) and a low contrast Bailey-Lovie chart (LCBL) were compared with clinical contrast sensitivity function (CSF) measurements in a group of normal subjects with a wide range of refractive errors We found high and significant correlations for the measurements obtained with the visual acuity tests, and between measurements obtained with the acuity tests and the CSF chart These results indicate that the CSF test provides little additional information as a screening test in routine practice, and could probably be restricted in its use to patients in whom ocular disease is suspected

Psychophysical measurement of neural adaptation abnormalities in magnocellular and parvocellular pathways in glaucoma.

Abstract: PURPOSE. It is well established that contrast sensitivity is reduced in glaucoma. This study explored whether such contrast processing abnormalities consist of an absolute threshold level difference or a problem with contrast gain control. METHODS. Seventeen patients with primary open-angle glaucoma and 17 approximately age-matched control subjects participated. Subjects were tested foveally and midperipherally (12.5°). Subjects with glaucoma were tested in a peripheral region of relatively normal visual field (neighboring locations required to be within the normal 95% confidence limit on the total deviation plot of their most recent SITA/full threshold Humphrey Field Analyzer assessment; Carl Zeiss Meditec, Dublin, CA). Control subjects were tested in matching locations. Contrast discrimination was assessed using the steady-pedestal (magnocellular [M] pathway) and pulsed-pedestal (parvocellular [P] pathway) stimuli of Pokorny and Smith for seven pedestal luminances between 15 and 75 cd/m 2 , presented on a background of 30 cd/m 2 . RESULTS. Glaucoma group thresholds were significantly elevated compared with control subjects foveally and peripherally on both the pulsed-pedestal (P) and steady-pedestal (M) tasks (P 0.01). Effect size statistics revealed slightly greater deficits on the P pathway task and greater deficits for pedestals that were decrements, rather than increments, from the surround luminance. Foveal deficits were of a magnitude to be explained by a reduction in contrast sensitivity; however, the peripheral deficits were greater than predicted by this factor alone. CONCLUSIONS. Foveal and midperipheral dysfunction of both M and P pathways was identified in people with glaucoma, in areas of relatively normal visual field performance. These findings are supportive of nonselective neural adaptation abnormalities in early glaucoma. (Invest Ophthalmol Vis Sci. 2004; 45:1846 –1853) DOI:10.1167/iovs.03-1225