Perception of global image contrast involves transparent spatial filtering and the integration and suppression of local contrasts (not RMS contrast)

Meese, Timothy S, Baker, Daniel H and Summers, Robert J (2017). Perception of global image contrast involves transparent spatial filtering and the integration and suppression of local contrasts (not RMS contrast). Royal Society Open Science, 4 (9),

Abstract

When adjusting the contrast setting on a television set, we experience a perceptual change in the global image contrast. But how is that statistic computed? We addressed this using a contrast-matching task for checkerboard configurations of micro-patterns in which the contrasts and spatial spreads of two interdigitated components were controlled independently. When the patterns differed greatly in contrast, the higher contrast determined the perceived global contrast. Crucially, however, low contrast additions of one pattern to intermediate contrasts of the other caused a paradoxical reduction in the perceived global contrast. None of the following metrics/models predicted this: max, linear sum, average, energy, root mean squared (RMS), Legge and Foley. However, a nonlinear gain control model, derived from contrast detection and discrimination experiments, incorporating wide-field summation and suppression, did predict the results with no free parameters, but only when spatial filtering was removed. We conclude that our model describes fundamental processes in human contrast vision (the pattern of results was the same for expert and naive observers), but that above threshold— when contrast pedestals are clearly visible—vision’s spatial filtering characteristics become transparent, tending towards those of a delta function prior to spatial summation. The global contrast statistic from our model is as easily derived as the RMS contrast of an image, and since it more closely relates to human perception, we suggest it be used as an image contrast metric in practical applications.

Publication DOI: https://doi.org/10.1098/rsos.170285
Divisions: Life & Health Sciences > Optometry
Life & Health Sciences > Clinical and Systems Neuroscience
Life & Health Sciences
Life & Health Sciences > Vision, Hearing and Language
Life & Health Sciences > Centre for Vision and Hearing Research
Life & Health Sciences > Psychology
Additional Information: © 2017 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited. Funding: EPSRC grant EP/H000038.
Uncontrolled Keywords: human vision ,contrast summation,Battenbergs,contrast gain control,image processing,psychophysics,General
Published Date: 2017-09-06
Authors: Meese, Timothy S ( 0000-0003-3744-4679)
Baker, Daniel H
Summers, Robert J ( 0000-0003-4857-7354)

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