• Chromaticity diagram is a convenient space coordinate representation of all the spectral colours and their mixtures based on the tri-stimulus values of the primary colours contained by them. Figure below is a two dimensional representation of hue and saturation in the X-Y plane. If a three dimensional representation is drawn, the ‘Z’ axis will show relative brightness of the colour.

Diagram:

• As seen in the figure the chromaticity diagram is formed by all the rainbow colours arranged along a horseshoe-shaped triangular curve. The various saturated pure spectral colours are represented along the perimeter of the curve, the corners representing the three primary colours—red, green and blue.
• As the central area of the triangular curve is approached, the colours become de-saturated representing mixing of colours or a white light. The white lies on the central point ‘C’ with coordinates x = 0.31 and y = 0.32. Actually there is no specific white light—sunlight, skylight, daylight are all forms of white light.
• The illuminant ‘C’ marked in figure represents a particular white light formed by combining hues having wavelength: 700 nm (red) 546.1 nm (green) and 438.8 nm (blue) with proper intensities.
• This shade of white which has been chosen to represent white in TV transmission and reception also corresponds to the subjective impression formed in the human eye by seeing a mixture of 30 percent of red colour, 59 percent of green colour and 11 percent of the blue colour at wavelengths specified above.
• A practical advantage of the chromaticity diagram is that, it is possible to determine the result of additive mixing of any two or more colour lights by simple geometric construction.

Advantages:

-A practical advantage of the chromaticity diagram is that, it is possible to determine the result of additive mixing of any two or more colour lights by simple geometric construction.

-The colour diagram contains all colours of equal brightness