Human Visual System

 Retina uses special cells called “rods” and “cones”. Rods “sees” in black, white & shades of grey and tell us the form or shape(Super-sensitive allowing us to see when it's very dark).Cones “senses” colour but need more light. Three types and each is sensitive to one of three different colours - red, green, or blue. Together these can sense combinations of light waves (To see millions of colours). Rods and cones together process the light to give you the total picture.

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PERCEPTION OF COLOUR

•         It involves a series of events which are interdisciplinary in nature. Perception of colours includes source of light, object that is illuminated and eye and brain that perceive the colour.

METAMERISM: It is a phenomenon observed when two specimens appears to have the similar colour under one set of viewing conditions, but different under another. The change in viewing conditions refers to change in source, observer or geometry of the observation.

TYPES OF METAMERISM

•         illuminant metamerism

•         observer metamerism

•         geometry metamerism

ILLUMINANT METAMERISM

•         When the colour of two specimens match under one illuminant but not with another illuminant, it is said to be illuminant metamerism.

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OBSERVER METAMERISM

•         When colour of two objects appear to match to one observer but not to the other, it is said to be observer metamerism. In this case observer may not be colour blind but the spectral sensitivity of colour receptors of one observer may be slightly different than the other.

GEOMETRY METAMERISM

•         Two objects which match in one arrangement of illumination, sample and observer may mismatch by altering the positions.