Lightness Constancy: A Direct Test of the Illumination-Estimation Hypothesis

2002 ◽  
Vol 13 (2) ◽  
pp. 142-149 ◽  
Author(s):  
M.D. Rutherford ◽  
D.H. Brainard
Keyword(s):  
Visual System ◽  
Color Constancy ◽  
The Other ◽  
Color Appearance ◽  
Direct Test ◽  
Illumination Estimation ◽  
Test Patch ◽  
Lightness Constancy ◽  
Surface Lightness

Many models of color constancy assume that the visual system estimates the scene illuminant and uses this estimate to determine an object's color appearance. A version of this illumination-estimation hypothesis, in which the illuminant estimate is associated with the explicitly perceived illuminant, was tested. Observers made appearance matches between two experimental chambers. Observers adjusted the illumination in one chamber to match that in the other and then adjusted a test patch in one chamber to match the surface lightness of a patch in the other. The illumination-estimation hypothesis, as formulated here, predicted that after both matches the luminances of the light reflected from the test patches would be identical. The data contradict this prediction. A second experiment showed that manipulating the immediate surround of a test patch can affect perceived lightness without affecting perceived illumination. This finding also falsifies the illumination-estimation hypothesis.

A Flying Gray Ball Multi-illuminant Image Dataset for Color Research

2020 ◽  
Vol 64 (5) ◽  
pp. 50411-1-50411-8
Author(s):  
Hoda Aghaei ◽  
Brian Funt
Keyword(s):  
Machine Vision ◽  
Spectral Reflectance ◽  
Color Constancy ◽  
Ground Truth ◽  
Practical Approach ◽  
Post Processing ◽  
Illumination Estimation ◽  
Processing Step ◽  
Image Dataset

Abstract For research in the field of illumination estimation and color constancy, there is a need for ground-truth measurement of the illumination color at many locations within multi-illuminant scenes. A practical approach to obtaining such ground-truth illumination data is presented here. The proposed method involves using a drone to carry a gray ball of known percent surface spectral reflectance throughout a scene while photographing it frequently during the flight using a calibrated camera. The captured images are then post-processed. In the post-processing step, machine vision techniques are used to detect the gray ball within each frame. The camera RGB of light reflected from the gray ball provides a measure of the illumination color at that location. In total, the dataset contains 30 scenes with 100 illumination measurements on average per scene. The dataset is available for download free of charge.

Color Constancy

2017 ◽  
Author(s):  
Joshua Gert
Keyword(s):  
Visual Representation ◽  
Color Constancy ◽  
Color Appearance ◽  
Fine Grained ◽  
Hybrid View

This chapter presents an account of color constancy that explains a well-known division in the data from color-constancy experiments: So-called “paper matches” exhibit a much higher level of constancy than so-called “hue-saturation matches.” It argues that the visual representation of objective color is the representation of something associated with a function from viewing circumstances to color appearances. Thus, a relatively robust constancy in the representation of objective color is perfectly consistent with a relatively less robust level of constancy in color appearance. The account also endorses Hilbert’s idea that we can represent the color of the illumination on a surface as well as the color of the surface itself. Finally, the chapter addresses an objection to the hybrid view that notes our capacity to make very fine-grained distinctions between the objective colors of surfaces.

Failure of color constancy for high luminance of a test patch that appears unnatural as an object in a space

2007 ◽  
Vol 14 (3) ◽  
pp. 139-144 ◽  
Author(s):  
Pontawee Pungrassamee ◽  
Mitsuo Ikeda ◽  
Aran Hansuebsai
Keyword(s):  
Color Constancy ◽  
High Luminance ◽  
Test Patch

Partial Color Constancy of Isolated Surface Colors Examined by a Color-Naming Method

Perception ◽  
1989 ◽  
Vol 18 (1) ◽  
pp. 83-91 ◽  
Author(s):  
Keiji Uchikawa ◽  
Hiromi Uchikawa ◽  
Robert M Boynton
Keyword(s):  
Color Constancy ◽  
Color Naming ◽  
The State ◽  
Color Appearance ◽  
Chromatic Adaptation ◽  
Light Sources ◽  
Two Factors ◽  
The Subject ◽  
Spectral Distributions ◽  
Color Scales

Color samples selected from the OSA Uniform Color Scales set were viewed without any surround. Separate light sources were used to illuminate the samples and to control the state of adaptation of the subject, thereby separating two factors that are normally confounded. A color-naming procedure was used to assess shifts in color appearance produced by altering the spectral distributions of one or both light sources. The results confirm that chromatic adaptation, when it is the only factor operating, can mediate partial color constancy.

scholarly journals The neural basis of lightness and color constancy in the visual system

2011 ◽  
Vol 11 (11) ◽  
pp. 351-351
Author(s):  
P. J. Kohler ◽  
S. V. Fogelson ◽  
E. A. Reavis ◽  
P. U. Tse
Keyword(s):  
Visual System ◽  
Color Constancy ◽  
Neural Basis

scholarly journals Optical axes of catadioptric systems including visual, Purkinje and other nonvisual systems of a heterocentric astigmatic eye

2010 ◽  
Vol 69 (3) ◽  
Author(s):  
W. F. Harris
Keyword(s):  
Visual System ◽  
Optical Axis ◽  
The Other ◽  
Optical Systems ◽  
Numerical Examples ◽  
Straight Line ◽  
Optical Axes ◽  
Catadioptric Systems ◽  
Reflecting Surfaces ◽  
Special Case

For a dioptric system with elements which may be heterocentric and astigmatic an optical axis has been defined to be a straight line along which a ray both enters and emerges from the system.  Previous work shows that the dioptric system may or may not have an optical axis and that, if it does have one, then that optical axis may or may not be unique.  Formulae were derived for the locations of any optical axes.  The purpose of this paper is to extend those results to allow for reflecting surfaces in the system in addition to refracting elements.  Thus the paper locates any optical axes in catadioptric systems (including dioptric systems as a special case).  The reflecting surfaces may be astigmatic and decentred or tilted.  The theory is illustrated by means of numerical examples.  The locations of the optical axes are calculated for seven optical systems associated with a particular heterocentric astigmatic model eye.  The optical systems are the visual system, the four Purkinje systems and two other nonvisual systems of the eye.  The Purkinje systems each have an infinity of optical axes whereas the other nonvisual systems, and the visual system, each have a unique optical axis. (S Afr Optom 2010 69(3) 152-160)

scholarly journals Transmission of ocular media in labrid fishes

2000 ◽  
Vol 355 (1401) ◽  
pp. 1257-1261 ◽  
Author(s):  
Ulrike E. Siebeck ◽  
N. Justin Marshall
Keyword(s):  
Visual System ◽  
Great Barrier Reef ◽  
Florida Keys ◽  
The Other ◽  
Barrier Reef ◽  
Functional Roles ◽  
Shallow Reef ◽  
Transmission Properties ◽  
Ocular Media ◽  
Transmission Measurements

Wrasses (Labridae) are the second largest family of fishes on the Great Barrier Reef (after the Gobiidae) and, in terms of morphology and lifestyle, one of the most diverse. They occupy all zones of the reef from the very shallow reef flats to deep slopes, feeding on a variety of fauna. Many wrasses also have elaborately patterned bodies and reflect a range of colours from ultraviolet (UV) to far red. As a first step to investigating the visual system of these fishes we measured the transmission properties of the ocular media of 36 species from the Great Barrier Reef, Australia, and Hawaii, California and the Florida Keys, USA. Transmission measurements were made of whole eyes with a window cut into the back, and also of isolated lenses and corneas. Based on the transmission properties of the corneas the species could be split into two distinct groups within which the exact wavelength of the cut–off was variable. One group had visibly yellow corneas, while the corneas of the other group appeared clear to human observers. Five species had ocular media that transmitted wavelengths below 400 nm, making a perception of UV wavelengths for those species possible. Possible functional roles for the different filter types are discussed.

Opposition fragmentation facilitates electoral accountability. Evidence from a survey experiment

2021 ◽  
pp. 135406882110524
Author(s):  
Sergi Ferrer
Keyword(s):  
The Other ◽  
Survey Experiment ◽  
Direct Test ◽  
Electoral Accountability ◽  
Other Hand ◽  
Original Survey ◽  
The One

Which is better for electoral accountability: a fragmented opposition that gives plenty of alternatives or an opposition with fewer stronger parties? While oppositions play a key role in democracies, the effect of opposition fragmentation on accountability remains unclear. On the one hand, fragmentation may enhance accountability by providing voters with ideologically close alternatives. On the other hand, increased fragmentation could make coordination over strong viable alternatives more difficult. In this study, I present an original survey experiment designed to test whether fragmentation of the opposition enhances accountability. Moreover, to assess the specific conditions under which fragmentation may enhance accountability, I distinguish between ideologues and pragmatic voters, and differentiate between ideological and valence issues. Results show that opposition fragmentation enhances accountability, particularly for ideologues. Lastly, I present a direct test of the mechanisms that demonstrates that fragmentation improves accountability because marginal gains in ideological proximity outweigh losses in viability.

If vision is “veridical hallucination,” what keeps it veridical?

2003 ◽  
Vol 26 (4) ◽  
pp. 426-427
Author(s):  
Peter Ulric Tse
Keyword(s):  
Visual System ◽  
Reference Frame ◽  
Physical Stability ◽  
The Other ◽  
Data Loss ◽  
Missing Information

If perception is constructed, what keeps perception from becoming mere hallucination unlinked to world events? The visual system has evolved two strategies to anchor itself and correct its errors. One involves completing missing information on the basis of knowledge about what most likely exists in the scene. For example, the visual system fills in information only in cases where it might be responsible for the data loss. The other strategy involves exploiting the physical stability of the environment as a reference frame with respect to which the eyes and body can move.

Spatial phenomenology requires potential illumination

2003 ◽  
Vol 26 (4) ◽  
pp. 425-426
Author(s):  
James A. Schirillo
Keyword(s):  
Visual System ◽  
Spatial Model ◽  
Dimensional Space ◽  
Color Constancy ◽  
Three Dimensional ◽  
Two Dimensions ◽  
Three Dimensional Space

Collapsing three-dimensional space into two violates Lehar's “volumetric mapping” constraint and can cause the visual system to construct illusory transparent regions to replace voxels that would have contained illumination. This may underlie why color constancy is worse in two dimensions, and argues for Lehar to revise his phenomenal spatial model by putting “potential illumination” in empty space.

Sign in / Sign up

Export Citation Format

Share Document