14Principles of Colour Photography

Materials that reflect light uniformly through the visible spectrum appear neutral, that is white, grey or black depending on the reflectance. A reflectance of 1 indicates that 100 per cent of the light is reflected, and the object appears perfectly white. Conversely, a zero reflectance indicates a perfect black. A reflectance of 0.20 corresponds to a mid-grey tone reflecting 20 per cent of the incident light. However, equal visual steps between black and white are not represented by equal steps in reflectance.

The sensation of colour arises from the selective absorption of certain wavelengths of light. Thus a coloured object reflects or transmits light unequally at different wavelengths. Reflectance varies ...

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