Lightness, brightness, and brightness contrast: 1. Illuminance variation (original) (raw)
Related papers
Lightness, brightness, and brightness contrast: 2. Reflectance variation
Attention Perception & Psychophysics, 1993
Changes of annulus luminance in traditional disk-and-annulus patterns can be perceived to be either reflectance or illuminance changes. In the present experiments, we examined the effect of varying annulus reflectance. In Experiment 1, we placed test and standard patch-and-surround patterns in identical Mondrian patchworks. Only the luminance of the test surround changed from trial to trial, appearing as reflectance variation under constant illumination. Lightness matches were identical to brightness matches, as expected. In Experiment 2, we used only the patch and surround (no Mondrian). Instructions said that the illumination would change from trial to trial. Lightness and brightness-contrast data were identical; illumination gradients were indistinguishable from reflectance gradients. In Experiment 3, the patterns were the same, but the instructions said that the shade of gray of the test surround would change from trial to trial. Lightness matches were identical to brightness matches, again confirming the ambiguity of diskand-annulus patterns.
Lightness constancy and illumination discounting
Attention Perception & Psychophysics
Contrary to the implication of the term “lightness constancy”, asymmetric lightness matching has never been found to be perfect unless the scene is highly articulated (i.e., contains a number of different reflectances). Also, lightness constancy has been found to vary for different observers, and an effect of instruction (lightness vs. brightness) has been reported. The elusiveness of lightness constancy presents a great challenge to visual science; we revisit these issues in the following experiment, which involved 44 observers in total. The stimuli consisted of a large sheet of black paper with a rectangular spotlight projected onto the lower half and 40 squares of various shades of grey printed on the upper half. The luminance ratio at the edge of the spotlight was 25, while that of the squares varied from 2 to 16. Three different instructions were given to observers: They were asked to find a square in the upper half that (i) looked as if it was made of the same paper as that on which the spotlight fell (lightness match), (ii) had the same luminance contrast as the spotlight edge (contrast match), or (iii) had the same brightness as the spotlight (brightness match). Observers made 10 matches of each of the three types. Great interindividual variability was found for all three types of matches. In particular, the individual Brunswik ratios were found to vary over a broad range (from .47 to .85). That is, lightness matches were found to be far from veridical. Contrast matches were also found to be inaccurate, being on average, underestimated by a factor of 3.4. Articulation was found to essentially affect not only lightness, but contrast and brightness matches as well. No difference was found between the lightness and luminance contrast matches. While the brightness matches significantly differed from the other matches, the difference was small. Furthermore, the brightness matches were found to be subject to the same interindividual variability and the same effect of articulation. This leads to the conclusion that inexperienced observers are unable to estimate both the brightness and the luminance contrast of the light reflected from real objects lit by real lights. None of our observers perceived illumination edges purely as illumination edges: A partial Gelb effect (“partial illumination discounting”) always took place. The lightness inconstancy in our experiment resulted from this partial illumination discounting. We propose an account of our results based on the two-dimensionality of achromatic colour. We argue that large interindividual variations and the effect of articulation are caused by the large ambiguity of luminance ratios in the stimulus displays used in laboratory conditions.
The Appearance of Brightness and Lightness
Final program and proceedings, 2000
In simplest terms, brightness is the appearance of luminance and lightness is the appearance of objects. The experiments in this paper measure the appearance of three visible faces of a real cube in real-life illumination. Three faces of the cube are painted white and the other three are painted different shades of gray. When the observer sees three white faces the experiment measures the appearance of illumination. When the experimenter rotates the cube to make visible a face with a different reflectance in the same illumination, then the experiment measures the appearance of objects. The results of matching experiments show that humans make the same match for luminance changes caused by illumination as those caused by reflectance. Humans can successfully recognize changes in whites due to illumination. They mistakenly interpret reflectance changes as illuminant position changes. However, in the same image they make the same matches for dark areas that were caused by illumination, reflectance or both.
The perception of luminosity on different backgrounds and in different illuminations
Perception, 1994
Observers were presented with target surfaces of varying luminance and asked to report whether they appeared luminous or opaque. In one experiment the targets were presented against three backgrounds, white, gray, and black. In another experiment the targets were presented within Mondrian patterns that were either brightly or dimly illuminated. The results indicate that, across a variety of conditions, a target begins to appear luminous when its luminance is about 1.7 times that of a surface that would appear white in the same illumination, whether or not a white surface is available in the visual field for comparison. Defined in this way the luminosity threshold exhibits the two main kinds of constancy characteristic of surface grays, constancy with respect to changes in the illumination level and constancy with respect to changes in the reflectance of the immediate background. This finding, while challenging a range of potential rules, places the problem of defining the conditions...
Lightness Constancy and its link with Cone Contrast
The link between chromatic constancy (compensation for hue and saturation shifts) and lightness constancy (compensation for a change in surface reflectance) was tested theoretically by computing cone contrasts and by asymmetric matching experiments. The effect of a thin achromatic line (a frame) around the test sample was tested empirically. When the samples were outlined by the frame, lightness constancy was increased and chromatic constancy reduced (p < 0.001). Changes in luminance are more likely to be compensated when the luminance contrast edge around the test stimulus is disturbed as with the addition of an achromatic frame.
What is the relationship between lightness and perceived illumination
Journal of Experimental Psychology: Human Perception and Performance
Surface reflectance and illumination level, which are confounded in the retinal image, must be disentangled by the visual system and a theory of lightness must explain how. Thus, a theory of surface lightness should also be a theory of perceived illumination and describe the relationship between them. Perceived illumination and perceived grey values have been measured using a new technique. Looking into a vision tunnel, observers saw two square apertures in the far wall, each revealing a patch of wall composed of two shades of grey. They adjusted the illumination level in one aperture to match that in the other. The stimuli placed in the apertures varied in luminance range, spatial frequency, and relative area. Results show that 1) illumination is matched for highest luminance (with no effect of spatial frequency). Combined with earlier findings that lightness is anchored by highest luminance, this supports Koffka's suggestion that lightness and perceived illumination are coupled in an invariant way. 2) Changes in the relative area of the light and dark shades produced complementary influences on perceived illumination and surface lightness. That is, when stimulus conditions evoke a conflict between anchoring the highest luminance at white and anchoring the largest area at white, enlarging the darker shade causes its lightness to increase and the perceived illumination to decrease by the same amount,
2020
The term simultaneous lightness constancy describes the capacity of the visual system to perceive equal reflecting surfaces as having the same lightness despite lying in different illumination fields. In some cases, however, a simultaneous lightness failure occurs, that is equal reflecting surfaces appear different in lightness when differently illuminated. An open question is if the luminance profile of the illumination edges affects simultaneous lightness constancy even when the ratio invariance property of the illumination edges is preserved. To explore this issue, we run two experiments by using bipartite illumination displays. Both the luminance profile of an illumination edge and the luminance ratio amplitude between the illumination fields were manipulated. Results revealed that the simultaneous lightness constancy increases when the luminance profile of the illumination edge is gradual (rather than sharp) and homogenous (rather than inhomogeneous), whilst it decreases when t...