Technology emulates and deceives the eye

Technical devices designed to capture light, such as CCDs in digital cameras, operate on the same principle as the eye by measuring the amounts of red, green and blue light entering it. As the total amount is related to the brightness of light, the relative amounts of the component colours can be used to calculate the colour of the light. On a TV screen or computer display, the full spectrum of colours can be made visible to the eye because of, or rather due to its functional limitations. By combining the three primary colours in different ways, the eye is tricked into perceiving an extensive range of colours. The eye cannot tell whether it is seeing an individual colour as its equivalent wavelength, or whether the light contains a suitable mixture of red, blue and green. For example, some video projectors operate by superimposing three primary colour images precisely on top of one another.

Nor is the accuracy of our vision absolute, as minute details are only detected to a limited extent. Due to this limitation of the eye, colours can also be produced with a dense pattern of small dots of primary colours arranged side by side. Again, the eye is unable to distinguish whether the TV screen displays either yellow colour or small red and green pixels in rapid succession. For all practical purposes, it is then sufficient to generate three primary colours, as the eye is tricked into perceiving their mixtures as an extensive range of colours. The RGB colour system is also called additive, as it produces individual colours by increasing the intensity of light when combining primary colours. Yellow can be generated by adding red to green, for example. With paints, the situation is completely different.

Close-up of a flat computer screen. The image and its colours are composed of three different coloured stripes of light.
Close-up of a TV screen. The colour pixels are so small that the eye sees an unbroken surface at normal viewing distances.

 RGB light Additive mixing of primary colours: red combined with blue produces magenta, blue added to green produces cyan, and green combined with red produces yellow. When all colours are combined, the result is white.

  In the colour wheel, colours in between the primary RGB colours are obtained by combining coloured light waves. Opposing colours are called complimentary colours.