The benefits of colour
When light hits a solid object, it can either be reflected or absorbed. An object that absorbs all the light hitting it will look black. One that reflects all light will look white. Intermediate levels of reflectance [reflectance the relative proportion of each wavelength reflected by a surface: the higher the reflectance, the lighter the object will look] (the term given to the ratio of incident to reflected light) will elicit shades between black and white. Also, objects reflect different amounts of light at different wavelengths. So the ability to distinguish between the amounts of different wavelengths of light reaching us from a given surface can convey a lot of information about the composition of the surface, without us having to come close to it. This is the basis of colour vision. It is possible to tell whether a fruit is ripe or not, or whether meat is safe to eat or putrid, using the colour i mation from the surface of the fruit or meat. Equally, it is possible to break camouflage. The ripe fruit is virtually invisible in the monochrome version because its luminance [luminance the intensity of light corrected for the degree to which the visual system responds to different wavelengths] (the amount of light that comes to us from it) is not sufficiently different from the canopy of leaves that surround it, the canopy serving as camouflage because it contains large random fluctuations in luminance. As soon as colour is added, we can see the fruit clearly. It has been argued (Osorio & Vorobyev, 1996; Sumner & Mollon, 2000) that the need to find fruit is the main reason for primates’ trichromatic colour vision. ‘Trichromatic’ simply means that there are three types of cone cells in the retina. Curiously, though, other mammals have only dichromatic colour vision, which means they only have two cone types – one corresp nding to medium-to-long wavelengths and another responding to short wavelengths. As a result, they cannot discriminate between objects that look green or red to us. So a red rag does not look particularly vivid to a bull! Interestingly, most animals (i.e. all birds and insects) have four cone types, one responding to UV radiation.
When light hits a solid object, it can either be reflected or absorbed. An object that absorbs all the light hitting it will look black. One that reflects all light will look white. Intermediate levels of reflectance [reflectance the relative proportion of each wavelength reflected by a surface: the higher the reflectance, the lighter the object will look] (the term given to the ratio of incident to reflected light) will elicit shades between black and white. Also, objects reflect different amounts of light at different wavelengths. So the ability to distinguish between the amounts of different wavelengths of light reaching us from a given surface can convey a lot of information about the composition of the surface, without us having to come close to it. This is the basis of colour vision. It is possible to tell whether a fruit is ripe or not, or whether meat is safe to eat or putrid, using the colour i mation from the surface of the fruit or meat. Equally, it is possible to break camouflage. The ripe fruit is virtually invisible in the monochrome version because its luminance [luminance the intensity of light corrected for the degree to which the visual system responds to different wavelengths] (the amount of light that comes to us from it) is not sufficiently different from the canopy of leaves that surround it, the canopy serving as camouflage because it contains large random fluctuations in luminance. As soon as colour is added, we can see the fruit clearly. It has been argued (Osorio & Vorobyev, 1996; Sumner & Mollon, 2000) that the need to find fruit is the main reason for primates’ trichromatic colour vision. ‘Trichromatic’ simply means that there are three types of cone cells in the retina. Curiously, though, other mammals have only dichromatic colour vision, which means they only have two cone types – one corresp nding to medium-to-long wavelengths and another responding to short wavelengths. As a result, they cannot discriminate between objects that look green or red to us. So a red rag does not look particularly vivid to a bull! Interestingly, most animals (i.e. all birds and insects) have four cone types, one responding to UV radiation.
No comments:
Post a Comment