Human estimation of local contrast orientation in natural images

Recently we found that the theories related to information theory existent in the literature cannot explain the behavior of the extent of the lateral inhibition mediated by retinal horizontal cells as a function of background light intensity. These theories can explain the fall of the extent from intermediate to high intensities, but not its rise from dim to intermediate intensities. We propose an alternate hypothesis that accounts for the extent's bell-shape behavior. This hypothesis proposes that the lateral-inhibition adaptation in the early retina is part of a system to extract several image attributes, such as occlusion borders and contrast. To do so, this system would use prior probabilistic knowledge about the biological processing and relevant statistics in natural images. A key novel statistic used here is the probability of the presence of an occlusion border as a function of local contrast. Using this probabilistic knowledge, the retina would optimize the spatial profile of lateral inhibition to minimize attribute-extraction error. The two significant errors that this minimization process must reduce are due to the quantal noise in photoreceptors and the straddling of occlusion borders by lateral inhibition.

Download Full-text

Detection of changes in the amplitude spectra of natural images is explained by a band-limited local-contrast model

10.1117/12.238712 ◽

1996 ◽

Cited By ~ 4

Author(s):

David J. Tolhurst ◽

Yoav Tadmor ◽

G. Arthurs

Keyword(s):

Natural Images ◽

Local Contrast ◽

Contrast Model ◽

Amplitude Spectra ◽

Band Limited

Download Full-text

Discrimination of Changes in the Slopes of the Amplitude Spectra of Natural Images: Band-Limited Contrast and Psychometric Functions

Perception ◽

10.1068/p261011 ◽

1997 ◽

Vol 26 (8) ◽

pp. 1011-1025 ◽

Cited By ~ 12

Author(s):

David J Tolhurst ◽

Yoav Tadmor

Keyword(s):

Spatial Frequency ◽

Discrimination Task ◽

Spatial Scales ◽

Natural Images ◽

Natural Scenes ◽

Local Contrast ◽

Frequency Bands ◽

Amplitude Spectra ◽

Lower Frequency Band ◽

Band Limited

Thresholds were measured for discriminating changes in the slopes of the amplitude spectra of stimuli derived from photographs of natural scenes and from random-luminance patterns. The variety and magnitudes of the thresholds could be explained by a model based on the discrimination of the changes in band-limited local contrast. Different spatial scales of local contrast (or different spatial-frequency bands of about 1 octave) were implicated for different reference spectral slopes; the model implicated a lower frequency-band for stimuli with shallower amplitude spectra. The implications of the model were tested experimentally by using stimuli in which the spectra were changed within restricted spatial-frequency bands. When the amplitude spectra of the test and reference stimuli differed only within the implicated frequency bands, thresholds were affected little. However, when the test and reference spectra differed at all frequencies except those in the implicated bands, the thresholds were elevated markedly. The forms of the psychometric functions for the discrimination task were entirely compatible with the hypothesis that the task relies upon the ability to discriminate changes of contrast. The Weibull functions fitted to the data had slope parameters (β) in the range 1 to 3, compatible with discrimination of low (but suprathreshold) contrasts.

Download Full-text

The statistics of local contrast and mean luminance in natural images

Journal of Vision ◽

10.1167/4.8.48 ◽

2004 ◽

Vol 4 (8) ◽

pp. 48-48

Author(s):

R. A. Frazor ◽

W. S. Geisler

Keyword(s):

Natural Images ◽

Local Contrast ◽

Mean Luminance

Download Full-text

Spatial structure, phase, and the contrast of natural images

10.1101/2021.06.16.448761 ◽

2021 ◽

Author(s):

Reuben Rideaux ◽

Rebecca K West ◽

Peter J Bex ◽

Jason B Mattingley ◽

William J Harrison

Keyword(s):

Spatial Structure ◽

Natural Images ◽

Natural Image ◽

Local Contrast ◽

Image Statistics ◽

Visual Neuroscience ◽

Environmental Statistics ◽

Phase Alignment ◽

Structure Phase ◽

Local Background

The sensitivity of the human visual system is thought to be shaped by environmental statistics. A major endeavour in visual neuroscience, therefore, is to uncover the image statistics that predict perceptual and cognitive function. When searching for targets in natural images, for example, it has recently been proposed that target detection is inversely related to the spatial similarity of the target to its local background. We tested this hypothesis by measuring observers' sensitivity to targets that were blended with natural image backgrounds. Importantly, targets were designed to have a spatial structure that was either similar or dissimilar to the background. Contrary to masking from similarity, however, we found that observers were most sensitive to targets that were most similar to their backgrounds. We hypothesised that a coincidence of phase-alignment between target and background results in a local contrast signal that facilitates detection when target-background similarity is high. We confirmed this prediction in a second experiment. Indeed, we show that, by solely manipulating the phase of a target relative to its background, the target can be rendered easily visible or completely undetectable. Our study thus reveals a set of image statistics that predict how well people can perform the ubiquitous task of detecting an object in clutter.

Download Full-text

Merging of electron-diffraction intensities acquired with a slow-scan CCD camera of crotoxin complex crystals to 3.5Å resolution

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100168256 ◽

1994 ◽

Vol 52 ◽

pp. 104-105

Author(s):

Jaap Brink ◽

Wah Chiu

Keyword(s):

Electron Diffraction ◽

Ccd Camera ◽

Crystal Thickness ◽

Local Contrast ◽

Camera Model ◽

Data Set ◽

3 Dimensional ◽

Diffraction Mode ◽

Diffraction Patterns ◽

Complex Crystals

Crotoxin complex is the principal neurotoxin of the South American rattlesnake, Crotalus durissus terrificus and has a molecular weight of 24 kDa. The protein is a heterodimer with subunit A assigneda chaperone function. Subunit B carries the lethal activity, which is exerted on both sides ofthe neuro-muscular junction, and which is thought to involve binding to the acetylcholine receptor. Insight in crotoxin complex’ mode of action can be gained from a 3 Å resolution structure obtained by electron crystallography. This abstract communicates our progress in merging the electron diffraction amplitudes into a 3-dimensional (3D) intensity data set close to completion. Since the thickness of crotoxin complex crystals varies from one crystal to the other, we chose to collect tilt series of electron diffraction patterns after determining their thickness. Furthermore, by making use of the symmetry present in these tilt data, intensities collected only from similar crystals will be merged.Suitable crystals of glucose-embedded crotoxin complex were searched for in the defocussed diffraction mode with the goniometer tilted to 55° of higher in a JEOL4000 electron cryo-microscopc operated at 400 kV with the crystals kept at -120°C in a Gatan 626 cryo-holder. The crystal thickness was measured using the local contrast of the crystal relative to the supporting film from search-mode images acquired using a 1024 x 1024 slow-scan CCD camera (model 679, Gatan Inc.).

Download Full-text