Journal ArticleDOI
Contrast in complex images.
TLDR
A definition of local band-limited contrast in images is proposed that assigns a contrast value to every point in the image as a function of the spatial frequency band and is helpful in understanding the effects of image-processing algorithms on the perceived contrast.Abstract:
The physical contrast of simple images such as sinusoidal gratings or a single patch of light on a uniform background is well defined and agrees with the perceived contrast, but this is not so for complex images. Most definitions assign a single contrast value to the whole image, but perceived contrast may vary greatly across the image. Human contrast sensitivity is a function of spatial frequency; therefore the spatial frequency content of an image should be considered in the definition of contrast. In this paper a definition of local band-limited contrast in images is proposed that assigns a contrast value to every point in the image as a function of the spatial frequency band. For each frequency band, the contrast is defined as the ratio of the bandpass-filtered image at the frequency to the low-pass image filtered to an octave below the same frequency (local luminance mean). This definition raises important implications regarding the perception of contrast in complex images and is helpful in understanding the effects of image-processing algorithms on the perceived contrast. A pyramidal image-contrast structure based on this definition is useful in simulating nonlinear, threshold characteristics of spatial vision in both normal observers and the visually impaired.read more
Citations
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Journal ArticleDOI
Contrast sensitivity to patch stimuli: effects of spatial bandwidth and temporal presentation
TL;DR: Measurements of the effects on the CSF of varying the spatial and temporal windows of grating patches are reported and it is demonstrated that the widely discrepant CSFs from previous studies can be accounted for by using these results.
Journal ArticleDOI
Spatial frequency and visual discomfort
Louise O'Hare,Paul B. Hibbard +1 more
TL;DR: Visual noise with a 1/f amplitude spectrum was judged more comfortable than any image with a relative increase in contrast energy within a narrow spatial frequency band, consistent with the idea that deviation from the statistics of natural images could cause discomfort.
Journal ArticleDOI
Automatic Exact Histogram Specification for Contrast Enhancement and Visual System Based Quantitative Evaluation
Debashis Sen,Sankar K. Pal +1 more
TL;DR: The effectiveness of the proposed automatic exact histogram specification technique in enhancing contrasts of images is demonstrated through qualitative analysis and the proposed image contrast measure based quantitative analysis.
Journal ArticleDOI
Erratum: Neural activity in areas V1, V2 and V4 during free viewing of natural scenes compared to controlled viewing (NeuroReport (January 15, 1998) 9:1)
TL;DR: The reduction of activity during free viewing relative to that obtained with flashed gratings is partly attributable to natural images being less effective stimuli and partly to suppressive spatio-temporal neural mechanisms that are important during natural vision.
Journal ArticleDOI
Pavlovian-to-Instrumental Transfer in Alcohol Dependence: A Pilot Study
Maria Garbusow,Daniel J. Schad,Christian Sommer,Elisabeth Jünger,Miriam Sebold,Eva Friedel,Jean Wendt,Norbert Kathmann,Florian Schlagenhauf,Florian Schlagenhauf,Ulrich S. Zimmermann,Andreas Heinz,Quentin J. M. Huys,Michael A. Rapp +13 more
TL;DR: The findings support an association of alcohol dependence with an increased propensity towards PIT and the implementation of PIT has favorably robust properties in chronic alcohol-dependent patients and in healthy controls.
References
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Relations between the statistics of natural images and the response properties of cortical cells.
TL;DR: The results obtained with six natural images suggest that the orientation and the spatial-frequency tuning of mammalian simple cells are well suited for coding the information in such images if the goal of the code is to convert higher-order redundancy into first- order redundancy.
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Spatial frequency selectivity of cells in macaque visual cortex
TL;DR: Among other things, it is shown that many stirate cells have quite narrow spatial bandwidths and at a given retinal eccentricity, the distribution of peak frequency covers a wide range of frequencies; these findings support the basic multiple channel notion.
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Chapter 9 Visual adaptation and retinal gain controls
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Feature Detection in Human Vision: A Phase-Dependent Energy Model
TL;DR: A simple and biologically plausible model of how mammalian visual systems could detect and identify features in an image is presented and it is suggested that the points in a waveform that have unique perceptual significance as ‘lines’ and ‘edges’ are the points where the Fourier components of the waveform come into phase with each other.
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Contrast constancy: deblurring in human vision by spatial frequency channels.
Mark A. Georgeson,G.D. Sullivan +1 more
TL;DR: It is argued that spatial frequency channels in the visual cortex are organized to compensate for earlier attenuation, and achieves a dramatic 'deblurring' of the image, and optimizes the clarity of vision.