RGB colour

RGB colour is an additive colour model in which red, green and blue light is combined in various proportions to reproduce a wide range of other colours. The name of the model comes from the initials of the three additive primary colours, red, green, and blue.

  • The human eye, and so human perception, is tuned to the visible spectrum and so to spectral colours between red and violet. However, because of the way the eye works, we can see many other colours which are produced by mixing colours from different areas of the spectrum. A particularly useful range of colours is produced by mixing red, green and blue light.
  • The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world.
  • A spectral colour is a colour corresponding with a single wavelength of visible light, or with a narrow band of adjacent wavelengths.
  • Except for the three RGB primary colours, RGB colours are not spectral colours because they are produced by combining colours from different areas of the visible spectrum.
  • Magenta is an example of an RGB colour for which there is no equivalent spectral colour.
  • RGB colour is a technology used to reproduce colour in ways that are well aligned with human perception. When an observer has separate controls allowing them to adjust the intensity of overlapping red, green and blue RGB primary coloured lights they are able to create a match for an extremely wide range of colours.
  • When looking at any modern display device such as a computer screen, mobile phone or video projector we are looking at RGB colour.
  • RGB colours are produced:
    • On a computer or mobile phone screen:  By Juxtaposing tiny dots of light corresponding with the three primary colours, red, green and blue.
    • On a digital projector: By projecting three carefully aligned but separate images, one red, one green and one blue onto a screen. Each image is made up of pixels of different intensity. Where the pixels from each image overlap they produce RGB colour by varying their relative intensity.
    • In computer software and apps: By selecting RGB colours using swatches or by selecting RGB colour values.

 

  • An extremely wide range of colours can be produced using RGB colour simply by varying the brightness of the three primary colours by different amounts.
  • The RGB colour model itself does not define what is meant by red, green and blue, and so the results of mixing them are relative to the choice of the particular red, green and blue lights that are used. When the exact chromaticity of the red, green, and blue primaries are defined, the colour model then becomes an absolute colour space, such as sRGB or Adobe RGB.
  • Look at a screen with large pixels (such as a TV) using a magnifying glass to see the three RGB primary colours. Then step back to see how they produce different colours when all the pixels merge together.
  • When working with a computer graphics application such as Adobe Illustrator, tints and shades can be produced by adjusting opacity in conjunction with white and black backgrounds.
  • Where an RGB colour model is used to control the output of a display device (computer screen, mobile phone or projector), tints are produced by increased the colour value of each RGB component proportionally, so increasing the intensity of the output, whilst shades are produced by proportionally decreasing the colour value of each RGB component, so decreasing the intensity of the output and dimming the output of the device.
  • RGB works by asking three questions of any colour: how red it is (R), how green it is (G), and how blue it is (B).
  • The RGB model is popular because it can easily be used to produce a comprehensive palette of 1530 spectral colours.
  • This RGB model is particularly useful where the output is to a web page or is to be presented on an RGB display device because of the system of notation that allows exact colours to be specified.

 

  • In the implementation of the RGB colour model used in Adobe Illustrator CC:
    • Colours can be selected using swatches which by default are identified by their decimal RGB values (right click a swatch to open Swatch Options).
    • Once a swatch has been selected right click on the icon for stoke/fill (top right of Swatches panel) and use the Color Picker to find a colour or adjust RGB (decimal and hex), HSB and CMYK values.

https://en.wikipedia.org/wiki/Comparison_of_color_models_in_computer_graphics