Topic
Contrast (vision)
About: Contrast (vision) is a research topic. Over the lifetime, 10379 publications have been published within this topic receiving 221480 citations.
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TL;DR: The proposed IQA scheme is designed to follow the masking effect and visibility threshold more closely, i.e., the case when both masked and masking signals are small is more effectively tackled by the proposed scheme.
Abstract: In this paper, we propose a new image quality assessment (IQA) scheme, with emphasis on gradient similarity. Gradients convey important visual information and are crucial to scene understanding. Using such information, structural and contrast changes can be effectively captured. Therefore, we use the gradient similarity to measure the change in contrast and structure in images. Apart from the structural/contrast changes, image quality is also affected by luminance changes, which must be also accounted for complete and more robust IQA. Hence, the proposed scheme considers both luminance and contrast-structural changes to effectively assess image quality. Furthermore, the proposed scheme is designed to follow the masking effect and visibility threshold more closely, i.e., the case when both masked and masking signals are small is more effectively tackled by the proposed scheme. Finally, the effects of the changes in luminance and contrast-structure are integrated via an adaptive method to obtain the overall image quality score. Extensive experiments conducted with six publicly available subject-rated databases (comprising of diverse images and distortion types) have confirmed the effectiveness, robustness, and efficiency of the proposed scheme in comparison with the relevant state-of-the-art schemes.
663 citations
TL;DR: Unitary responses to sinusoidal gratings either moving or alternating in phase have been investigated in the optic tract, lateral geniculate body and visual cortex of the cat as a function of the spatial frequency, position of the grating with respect to the cell receptive field and grating contrast.
658 citations
TL;DR: It is argued that the retinal goal is to transform the visual input as much as possible into a statistically independent basis as the first step in creating a redundancy reduced representation in the cortex, as suggested by Barlow.
Abstract: By examining the experimental data on the statistical properties of natural scenes together with (retinal) contrast sensitivity data, we arrive at a first principle, theoretical hypothesis for the purpose of retinal processing and its relationship to an animal's environment. We argue that the retinal goal is to transform the visual input as much as possible into a statistically independent basis as the first step in creating a redundancy reduced representation in the cortex, as suggested by Barlow. The extent of this whitening of the input is limited, however, by the need to suppress input noise. Our explicit theoretical solutions for the retinal filters also show a simple dependence on mean stimulus luminance: they predict an approximate Weber law at low spatial frequencies and a De Vries-Rose law at high frequencies. Assuming that the dominant source of noise is quantum, we generate a family of contrast sensitivity curves as a function of mean luminance. This family is compared to psychophysical data.
630 citations
TL;DR: Although differences in surface characteristics such as color, brightness, and texture can be instrumental in defining edges and can provide cues for visual search, they play only a secondary role in the real-time recognition of an intact object when its edges can be readily extracted.
614 citations
TL;DR: To examine the association between visual impairment and falls in older people, a large number of patients with visual impairment or severe visual impairment are referred to a rehabilitation clinic.
Abstract: OBJECTIVES: To examine the association between visual impairment and falls in older people.
DESIGN: Cross-sectional survey of eye disease with retrospective collection of falls data.
SETTING: Two postcode areas in the Blue Mountains west of Sydney, Australia.
PARTICIPANTS: All people 49 years of age and older were invited to participate, 3654 (82.4%) of 4433 eligible residents took part, and 3299 answered questions about falls.
MEASUREMENTS: Subjects had a detailed eye examination and answered questions about health and vision status, use of medication, and number of falls in the previous 12 months.
RESULTS: Tests of visual function that had a statistically significant association with two or more falls after adjustment for confounders were visual acuity (prevalence ratio (PR) 1.9 for visual acuity worse than 20/30), contrast sensitivity (PR 1.2 for a 1-unit decrease at 6 cycles per degree), and suprathreshold visual field screening (PR 1.5 for 5 or more points missing). However, only visual acuity and contrast sensitivity were significantly associated with two or more falls per 1 standard deviation decrease. The presence of posterior subcapsular cataract (PR 2.1) and use of nonmiotic glaucoma medication (PR 2.0) had a statistically significant association with two or more falls; presence of age-related macular degeneration, diabetic retinopathy, and cortical or nuclear cataract did not.
CONCLUSION: Visual impairment is strongly associated with two or more falls in older adults. In addition to poor visual acuity, visual factors such as reduced visual field, impaired contrast sensitivity, and the presence of cataract may explain this association.
607 citations