It has been proven that the absolute brightness information is of secondary importance to HVS and tends to be largely discarded on very early stages of visual processing through mechanisms of brightness constancy Local contrasts are used instead to convey the wealth of information about the scene [10].
The SDSS project entails systematically mapping one-quarter of the entire sky, producing a detailed image of it and determining the positions and absolute brightness of more than 100 million celestial objects, according to the scientists.