What Determines the Perceived Brightness of Objects?
What determines the perceived brightness of objects?
Luminance is a physical and objective measure of the intensity of light. The sensation elicited by different luminances is called brightness. However brightness is a subjective measure as it is the perceived amount of light emanating from an object. It may seem logical to expect that luminance and brightness are directly proportional and that two objects that reflect the same amount of physical light into the eye will look the same brightness. However, as this essay will discuss, the apparent brightness of objects is not entirely dependent upon the amount of light received from them and other factors are influential in the way we perceive brightness.
Our perception of the brightness of objects often depends more on the luminance of adjacent objects and backgrounds than on the actual luminance of the object itself. Two surfaces reflecting the same physical amount of light to the eyes typically look differently bright if the surfaces are observed in surrounds that are themselves returning different amounts of light. This phenomenon is called simultaneous brightness contrast.
This effect can be seen when two squares with exactly the same physical brightness are each surrounded by a larger square of different brightness. The square on the dark background appears lighter than the square on the light background. This can be seen in figure 1 below.
This effect can be explained by the centre/surround organisation of retinal ganglion cells. The organisation means that the response of the ganglion cell to stimulation of one portion of its receptive field, (the area to which a ganglion cell is sensitive), can be modified by stimulation of a neighbouring area. This interaction between antagonistic regions is caller lateral inhibition. If an ON-centre receptive field, that is the centre is stimulated by light and the surround is inhibited by light, is placed over the left square, the light in the
Luminance is a physical and objective measure of the intensity of light. The sensation elicited by different luminances is called brightness. However brightness is a subjective measure as it is the perceived amount of light emanating from an object. It may seem logical to expect that luminance and brightness are directly proportional and that two objects that reflect the same amount of physical light into the eye will look the same brightness. However, as this essay will discuss, the apparent brightness of objects is not entirely dependent upon the amount of light received from them and other factors are influential in the way we perceive brightness.
Our perception of the brightness of objects often depends more on the luminance of adjacent objects and backgrounds than on the actual luminance of the object itself. Two surfaces reflecting the same physical amount of light to the eyes typically look differently bright if the surfaces are observed in surrounds that are themselves returning different amounts of light. This phenomenon is called simultaneous brightness contrast.
This effect can be seen when two squares with exactly the same physical brightness are each surrounded by a larger square of different brightness. The square on the dark background appears lighter than the square on the light background. This can be seen in figure 1 below.
This effect can be explained by the centre/surround organisation of retinal ganglion cells. The organisation means that the response of the ganglion cell to stimulation of one portion of its receptive field, (the area to which a ganglion cell is sensitive), can be modified by stimulation of a neighbouring area. This interaction between antagonistic regions is caller lateral inhibition. If an ON-centre receptive field, that is the centre is stimulated by light and the surround is inhibited by light, is placed over the left square, the light in the
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