2.2.1 Colour Perception

Colours

In every day life, objects are described by particular colours, and often are identified with reference to familiar things. For example, as blue as the sky, as green as grass, as white as snow are common terms used to describe the colours. From the scientific perspective, the theory on the physics of colour began with Isaac Newton early in the 18th century. Using a prism, he separated sunlight into a spectrum of colours. He was able to distinguish seven colours: violet, indigo, blue, green, yellow, orange and red. Newton was able to separate rays of sunshine because light from different wavelengths is refracted by varying degrees when passing from one medium (air) to another (a crystal prism).

prism

visible spectrum

Wavelengths within the visible spectrum range from 400 to 700 nanometres. Within this spectrum an infinite number of colours can occur. A colour can vary in hue (chromaticity), intensity (brightness), or saturation (purity), separately, or in combination with the other components. It has been shown that with experience, humans can discriminate 120 or more hues when intensity and saturation are held constant. More, if intensity and saturation vary. However, with practical experiments scientists have shown that, most commonly, differentiation begins to break down when more than 7-12 colours along with black, white and grey tones are used at the same time in a display.

Hue, intensity and saturation