RGB & the trichromatic colour model

About RGB & the trichromatic colour model

To make sense of the physiological basis of the RGB colour model we can relate it to how the trichromatic colour model explains colour vision. Let’s look at the Trichromatic colour model first:

  • The trichromatic colour theory, which is also known as the Young-Helmholtz theory, established that there are three types of cone cells in the human eye that carry out the initial stage of colour processing that ultimately produces the world of colours we see around us.
  • Cone cells are daylight photoreceptors which means they are able to convert light into electrical charges through a process called photo-transduction.
  • The sensitivity of cone cells was established using spectroscopy which measures which wavelengths are absorbed and which are reflected.
  • The three types of cone cells were identified along with the range of wavelength they absorbed:
    • L = Long (500–700 nm)
    • M = Medium (440 – 670 nm)
    • S = Short (380 – 540 nm)
  • The trichromatic colour theory also established the visual effect of exposing a human observer to mixtures of light produced by three monochromatic light sources, one in the red, one in the green, and one in the blue part of the spectrum.
  • It proved that by incrementally adjusting the intensity of the light produced by each source an observer can be induced to see any colour within the visible spectrum.
  • The outcome was that a match was produced between how the L, M and S cone cells responded to light of different wavelengths and calibrated mixtures of wavelengths of light corresponding with R, G and B. This is the basis of the RGB colour model.
  • The fact that mixtures of red, green and blue light at different levels of intensity can be used to stimulate the L, M and S cones types to produce any human observable colour underpins almost every form of colour management in practice today.