A Colour Constancy Phenomenon Related to Perceived 3-D Shape

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 11-11
Author(s):  
S S Bergström ◽  
K-A Gustafsson ◽  
T Jakobsson
Keyword(s):  
Shape From Shading ◽  
Lower Half ◽  
The Other ◽  
Colour Filter ◽  
Colour Constancy ◽  
Psychophysical Data ◽  
Roof Shape

Flat, rectangular displays consisting of 2, 3, 4, or 6 vertical grey stripes, alternately light and dark gray (NCS 3500 and NCS 6000, respectively) were presented one at a time illuminated by two identical projectors. One projector illuminated the upper half of the display through a yellowish colour filter (Strand Golden Amber), and the other one illuminated the lower half through a bluish colour filter (Kodak Wratten 80 A). The display appeared ambiguous, periodically and spontaneously shifting between two distinct 3-D shape percepts, A and B. Display A appeared vertically folded along the reflectance edges (‘shape from shading’, where the dark fields appeared to be attached shadows). The colours were quite saturated yellow and blue surface colours. There was no colour constancy; Display B appeared horizontally folded along the illumination edge like a roof (‘shape from shading’, where one of the illuminations appeared to be an attached shadow). The display now appeared very desaturated, even achromatic, but in a ‘warm’ illumination. The colour constancy was almost complete. The phenomenon is demonstrated with a slide, and some psychophysical data on the colour desaturation and on the frequency of shifts between the two percepts are reported as well as some observations on combinations of illuminant colours other than yellow and blue. The reported colour constancy phenomenon is discussed in relation to an earlier presented model for the perception of illumination, colour, and depth [S S Bergström, 1994, in Lightness, Brightness, and Transparency Ed. A Gilchrist (Hillsdale, NJ: Lawrence Erlbaum Associates)].

Ambiguities in Colour Constancy and Shape from Shading

Perception ◽  
1997 ◽  
Vol 26 (4) ◽  
pp. 531-541 ◽  
Author(s):  
Torbjörn Jakobsson ◽  
Sten Sture Bergström ◽  
Karl-Arne Gustafsson ◽  
Elena Fedorovskaya
Keyword(s):  
Shape From Shading ◽  
The Other ◽  
Colour Constancy ◽  
Stimulus Situation ◽  
Descriptive Data ◽  
Visual Phenomenon ◽  
Sharp Edges ◽  
Grey Colour ◽  
Surprising Observation

A new visual phenomenon—called the AMBEGUJAS phenomenon—is presented, together with some descriptive data from two initial exploratory experiments. The phenomenon is basically one of shape from shading, but ambiguous as to both shape and colour. There are two spontaneously alternating and mutually exclusive perceived 3-D shapes, and—as the most surprising observation—the colour impressions of these two shapes are markedly different. The stimulus situation is very simple with two differently coloured illuminations (with sharp edges) adjacently cast onto a flat, grey striped surface. In one 3-D shape almost the whole chromatic content disappears, and the surface goes towards its veridically grey colour. In the other the perceived object assumes the two illumination colours as clear surface colours. The decolorised percept is interpreted as a striking example of colour constancy: a perceptual solution with the classical ‘discounting of the illuminant’. Experiments show that the phenomenon is robust and appears in varying display layouts and different combinations of chromatic illuminations.

Measurements of Colour Constancy by Using a Forced-Choice Matching Technique

Perception ◽  
1996 ◽  
Vol 25 (2) ◽  
pp. 229-241 ◽  
Author(s):  
David I Bramwell ◽  
Anya C Hurlbert
Keyword(s):  
Forced Choice ◽  
The Other ◽  
Two Dimensional ◽  
Colour Constancy ◽  
Test Patch ◽  
Complex Scenes ◽  
Matching Technique ◽  
Chromatic Sensitivity ◽  
Colour Appearance ◽  
Method Of Constant Stimuli

Colour constancy is typically measured with techniques involving asymmetric matching by adjustment, in which the observer views two scenes under different illuminants and adjusts the colour of a reference patch in one to match a test patch in the other. This technique involves an unnatural task, requiring the observer to predict and adjust colour appearance under an illumination shift. Natural colour constancy is more a simple matter of determining whether a colour is the same as or different from that seen under different illumination conditions. There are also technical disadvantages to the method of matching by adjustment, particularly when used to measure colour constancy in complex scenes. Therefore, we have developed and tested a two-dimensional method of constant-stimuli, forced-choice matching paradigm for measuring colour constancy. Observers view test and reference scenes haploscopically and simultaneously, each eye maintaining separate adaptation throughout a session. On each trial, a pair of test and reference patches against multicoloured backgrounds are presented, the reference patch colours being selected from a two-dimensional grid of displayable colours around the point of perfect colour constancy. The observer's task is to respond “same” or “different”. Fitting a two-dimensional Gaussian to the percentage of “different” responses yields (1) the subjective colour-constancy point, (2) the discrimination ellipse centred on this point, and (3) a map of changes in sensitivity to chromatic differences induced by the illuminant shift. The subjective colour-constancy point measured in this way shows smaller deviations from perfect colour constancy—under conditions of monocular adaptation—than previously reported; discrimination ellipses are several times larger than standard MacAdam ellipses; and chromatic sensitivity is independent of the direction of the illuminant shift, for broad distributions of background colours.

A second species of the genus Blythia Theobald, 1868 (Squamata: Colubridae) from Mizoram, India

Zootaxa ◽  
2017 ◽  
Vol 4276 (4) ◽  
pp. 569 ◽  
Author(s):  
GERNOT VOGEL ◽  
HMAR TLAWMTE LALREMSANGA ◽  
VANLALHRIMA VANLALHRIMA
Keyword(s):  
Tail Length ◽  
Lower Half ◽  
The Other ◽  
Morphological Data ◽  
Total Length ◽  
Bright Orange

A second species of the genus Blythia Theobald, 1868, Blythia hmuifang sp. nov., is described on the basis of four specimens originating from Mizoram, India. It differs from Blythia reticulata, the other known species in the genus, by having fewer ventral scales (114–117 vs. 129–149), by having fewer subcaudal scales in males (20–21 vs. 22–32), by the greater proportion of tail length/total length (0.109–0.116 vs. 0.075–0.098), by the colour of the venter (bright orange-red in smaller specimens, cream in the largest specimen vs. black in all ages) and the colouration of the supralabials (lower half pale vs. dark), plus other smaller differences in the colouration and the hemipenis. The distribution of Blythia reticulata is discussed. Morphological data of eight recently collected specimens from Mizoram are given and compared to other populations. 

Colour Constancy as Measured by Least Dissimilar Matching

2011 ◽  
Vol 24 (5) ◽  
pp. 407-452 ◽  
Author(s):  
Alexander D. Logvinenko ◽  
Rumi Tokunaga
Keyword(s):  
Visual System ◽  
Stimulus Display ◽  
Statistical Test ◽  
The Other ◽  
Colour Constancy ◽  
Exact Match ◽  
Match Rate ◽  
Black Paper ◽  
Colour Match

AbstractAlthough asymmetric colour matching has been widely used in experiments on colour constancy, an exact colour match between objects lit by different chromatic lights is impossible to achieve. We used a modification of this technique, instructing our observers to establish the least dissimilar pair of differently illuminated coloured papers. The stimulus display consisted of two identical sets of 22 Munsell papers illuminated independently by neutral, yellow, blue, green and red lights. The lights produced approximately the same illuminance. Four trichromatic observers participated in the experiment. The proportion of exact matches was evaluated. When both sets of papers were lit by the same light, the exact match rate was 0.92, 0.93, 0.84, 0.78 and 0.76 for the neutral, yellow, blue, green and red lights, respectively. When one illumination was neutral and the other chromatic, the exact match rate was 0.80, 0.40, 0.56 and 0.32 for the yellow, blue, green and red lights, respectively. When both lights were chromatic, the exact match rate was found to be even poorer (0.30 on average). Yet, least dissimilar matching was found to be rather systematic. Particularly, a statistical test showed it was symmetric and transitive. The exact match rate was found to be different for different papers, varying from 0.99 (black paper) to 0.12 (purple paper). Such a variation can hardly be expected if observers' judgements were based on an illuminant estimate. We argue that colour constancy cannot be achieved for all the reflecting objects because of mismatching of metamers. We conjecture that the visual system might have evolved to have colour constant perception for some ecologically valid objects at a cost of colour inconstancy for other types of objects.

scholarly journals Visual acuity in light of different colours

1930 ◽  
Vol 106 (744) ◽  
pp. 276-292 ◽  
Keyword(s):  
Visual Acuity ◽  
Blue Light ◽  
Colour Vision ◽  
Quantitative Measurement ◽  
Bright Light ◽  
The Other ◽  
Stray Light ◽  
Colour Filter ◽  
Ground Glass ◽  
Two Sectors

Previous work on visual acuity has shown that there is a different law relating intensity of illumination to acuity of vision for lights of low and of high intensities. Hecht has recently discussed this problem (1) basing his discussion on the measurements of König (2). König obtained poor acuity of vision with “blue” light. In view of the importance to the study of colour vision of any method of quantitative measurement, the following experiments were undertaken. Method . A bright light (A, fig. 1) was concentrated by means of a condenser (B) on a colour filter (C) and the light was concentrated on a ground-glass screen (F) by means of a lens (E). Close to the lens was a shutter (D) consisting of two sectors, each with three apertures of 60°, so that when the two sectors were superimposed with the open parts opposite to each other half the lens was exposed to light, but when one shutter was rotated so that the opaque parts of it coincided with the apertures of the other, all the light ought to have been cut off. As a matter of fact some stray light found its way past when the shutter was supposed to be entirely closed, but the amount so passing was slight.

Unifying shading and texture through an active observer

1989 ◽  
Vol 238 (1290) ◽  
pp. 25-37 ◽  
Keyword(s):  
Three Dimensional ◽  
Shape From Shading ◽  
Surface Orientation ◽  
The Other ◽  
Simple Solution ◽  
Image Intensity ◽  
Other Hand ◽  
Shape From Texture ◽  
Perceptual Phenomenon

Shading (variations of image intensity) provides an important cue for understanding the shape of three-dimensional surfaces from monocular views. On the other hand, texture (distribution of discontinuities on the surface) is a strong cue for recovering surface orientation by using mon­ocular images. But given the image of an object or scene, what tech­nique should we use to recover the shape of what is imaged ? Resolution of shape from shading requires knowledge of the reflectance of the imaged surface and, usually, the fact that it is smooth (i. e. it shows no disconti­nuities). Determination of shape from texture requires knowledge of the distribution of surface markings (i. e. discontinuities). One might expect that one method would work when the other does not. I present a theory on how an active observer can determine shape from the image of an object or scene regardless of whether the image is shaded, textured, or both, and without any knowledge of reflectance maps or the distri­bution of surface markings. The approach is successful because the active observer is able to manipulate the constraints behind the perceptual phenomenon at hand and thus derive a simple solution. Several experi­mental results are presented with real and synthetic images.

Stromatoporoids from the Famennian (Devonian) Wabamun Formation, Normandville oilfield, north–central Alberta, Canada

1988 ◽  
Vol 62 (03) ◽  
pp. 411-419 ◽  
Author(s):  
Colin W. Stearn
Keyword(s):  
Patch Reef ◽  
Abundant Species ◽  
The Other ◽  
North Central ◽  
Biotic Crisis

Stromatoporoids are the principal framebuilding organisms in the patch reef that is part of the reservoir of the Normandville field. The reef is 10 m thick and 1.5 km2in area and demonstrates that stromatoporoids retained their ability to build reefal edifices into Famennian time despite the biotic crisis at the close of Frasnian time. The fauna is dominated by labechiids but includes three non-labechiid species. The most abundant species isStylostroma sinense(Dong) butLabechia palliseriStearn is also common. Both these species are highly variable and are described in terms of multiple phases that occur in a single skeleton. The other species described areClathrostromacf.C. jukkenseYavorsky,Gerronostromasp. (a columnar species), andStromatoporasp. The fauna belongs in Famennian/Strunian assemblage 2 as defined by Stearn et al. (1988).

D. The Line Spectrum of Pulsating Variable Stars

1967 ◽  
Vol 28 ◽  
pp. 207-244
Author(s):  
R. P. Kraft
Keyword(s):  
Variable Stars ◽  
The Other ◽  
Line Spectrum ◽  
Afternoon Session ◽  
Empirical Information ◽  
Pulsating Variable Stars ◽  
Almost Continuous ◽  
Informal Approach

(Ed. note:Encouraged by the success of the more informal approach in Christy's presentation, we tried an even more extreme experiment in this session, I-D. In essence, Kraft held the floor continuously all morning, and for the hour and a half afternoon session, serving as a combined Summary-Introductory speaker and a marathon-moderator of a running discussion on the line spectrum of cepheids. There was almost continuous interruption of his presentation; and most points raised from the floor were followed through in detail, no matter how digressive to the main presentation. This approach turned out to be much too extreme. It is wearing on the speaker, and the other members of the symposium feel more like an audience and less like participants in a dissective discussion. Because Kraft presented a compendious collection of empirical information, and, based on it, an exceedingly novel series of suggestions on the cepheid problem, these defects were probably aggravated by the first and alleviated by the second. I am much indebted to Kraft for working with me on a preliminary editing, to try to delete the side-excursions and to retain coherence about the main points. As usual, however, all responsibility for defects in final editing is wholly my own.)

C. The Continuous Spectrum of Pulsating Variable Stars

1967 ◽  
Vol 28 ◽  
pp. 177-206
Author(s):  
J. B. Oke ◽  
C. A. Whitney
Keyword(s):  
Continuous Spectrum ◽  
Variable Stars ◽  
Velocity Fields ◽  
The Other ◽  
Line Spectrum ◽  
Direct Information ◽  
Thermodynamic Structure ◽  
Diagnostic Interpretation ◽  
Pulsating Variable Stars ◽  
The Continuum

Pecker:The topic to be considered today is the continuous spectrum of certain stars, whose variability we attribute to a pulsation of some part of their structure. Obviously, this continuous spectrum provides a test of the pulsation theory to the extent that the continuum is completely and accurately observed and that we can analyse it to infer the structure of the star producing it. The continuum is one of the two possible spectral observations; the other is the line spectrum. It is obvious that from studies of the continuum alone, we obtain no direct information on the velocity fields in the star. We obtain information only on the thermodynamic structure of the photospheric layers of these stars–the photospheric layers being defined as those from which the observed continuum directly arises. So the problems arising in a study of the continuum are of two general kinds: completeness of observation, and adequacy of diagnostic interpretation. I will make a few comments on these, then turn the meeting over to Oke and Whitney.

Observing programme for the 24-inch/36-inch Schmidt telescope

1966 ◽  
Vol 24 ◽  
pp. 337
Author(s):  
W. Iwanowska
Keyword(s):  
The Other ◽  
Schmidt Telescope ◽  
Flint Glass

A new 24-inch/36-inch//3 Schmidt telescope, made by C. Zeiss, Jena, has been installed since 30 August 1962, at the N. Copernicus University Observatory in Toruń. It is equipped with two objective prisms, used separately, one of crown the other of flint glass, each of 5° refracting angle, giving dispersions of 560Å/mm and 250Å/ mm respectively.

Sign in / Sign up

Export Citation Format

Share Document