When viewed against a dark background, a gray patch appears brighter, and it appears darker when viewed against a background that is bright. Simultaneous contrast is the name of this effect. It is one of the many effects of brightness that are commonly ascribed to visual processes that are simple such as the lateral inhabitation that takes place in the retina, where adjacent cells are inhibited by cells in one region. A Retinex model, which is another class of models, has also been used to explain the perception of surface colors in regards to the information propagation about changes in local luminance. These two kinds of models are based on low-level processes involving simple connections between neighboring neurons. Such models’ output should not be affected by a higher-level perception properties display, such as the perceived form and depth. However, it has been found that a change in perpetual interpretation may have a weighty effect when it comes to judgment of brightness.
According to the customary terminology, lightness is the reflectance that is apparent of a scene surface, while brightness is the luminance of a patch that is apparent in the image itself. This means that an observer in an experiment of brightness is asked to make a judgment on the shade of ink on the page, but not to make any interpretations regarding the surfaces of the objects that have been portrayed. Through illustration, patches on a diagram may appear brighter as they are viewed as to have a higher luminance on the page as compared to patches that are not positioned in a place where they will be viewed as having high luminance on the page (Kimchi, Behrmann, &Olson 40).
High-level perceptual factors may also have an influence on judgments on lightness. This is easily illustrated when a geometry leads to a 3-D interpretation that makes some patches to match with lightness and not match with other patches that have the luminance. Perception of surface curvature can also affect lightness. Low –level models cannot be used in the explanation of these different phenomena on lightness. This is because a person observing in an experiment on lightness is making a judgment on the properties of the portrayed objects, instead of merely making estimation on the brightness of the ink on the page; it is not surprising to find that mechanisms that are low-leveled may fail to give an explanation to the results (Gilchrist).
An experiment was carried out using stimuli that were displayed on a computer screen, and a more sensory brightness judgment was used instead of the most perceptual judgment on lightness. Therefore, both the task and the stimuli ought to have favored low-level models success. However, low-level models did not succeed.
It is probable that grey-level junctions are important for the perceptual organization determination thereby the percepts of brightness and lightness. Therefore, for this reorganization, one promising class of models would involve constraints propagation from gray-level junctions. Corrugated plaid pattern may be used as another illustration. Each figure is gotten from a similar 5 by 5 matrix of gray –level in an orientation that is similar. This means, in the raster sequence, the upper left patch has a similar gray shade for each, and so on. Note should be taken that the images are not shown as rotated versions of each other. The shapes of the patches are the only notable difference. In both figures, the edge adjacency relationship and the grey-levels are identical.
Argyle illusion may be another effect. Two diamonds with the same shade of grey, which is also similar to the shade in the background, may be used to illustrate this effect. These patches are judged to have a brightness that is different. When observed on a monitor, the effect is so persuasive that most observers that are experienced fail to accept the correctness of that display. There is a sense of dark strips and light underlying the columns in this stimulus. The strips may be perceived, for instance, as transparent filters of dark shades and light. It is the report of subjects that the diamonds that appear as if covered by a light filter seem darker when compared to those that appear as if covered by a dark filter that appears brighter (Harris & Jenkin 40).
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From all the phenomena discussed above, a similar conclusion is reached. The conclusion is that a judgment on brightness cannot be explained by the use of low-level mechanisms. Dramatic changes in the report on brightness may be caused by geometrical changes that ought to be inconsequential for mechanisms that are low-leveled. It appears as though there is an automatic estimation of the reflectance of surfaces in the world and the lightness percepts that inevitably lead to the swaying of brightness judgment by the visual system. In the determination of the perceptual organization that is underlying these effects, constraints from junctions may be essential. A new set of illusions on brightness cannot be explained by low level models. In these illusions, perceptual organization of the stimuli strongly influences brightness percept. Simple stimuli modifications ought to have little effect on low-level mechanisms highly make an alternation on the strength of the illusion. For a model to make a prediction on the phenomena of brightness, it may require to use mechanisms that are sophisticated that ensure image decomposition into a set of intrinsic images that are a representation of reflectance, transparency and illumination.
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