color coding

Light is a combination of electromagnetic waves each characterized by its wavelength (or its frequency which is inversely proportional to it: F=c/L where c is the speed ... of light in the vacuum). Our eyes can only capture a tiny part of the light, visible light (wavelengths between 400 and 700 nanometers), but neither gamma, X and UV (ultraviolet) rays, nor IR (infrared) and radio waves.
A color is a representation, created by our brain, of waves picked up by specific cells of our retina: cones (three types which detect the presence of three wavelengths corresponding to blue , green and red) and sticks (sensitive to the intensity of light, especially useful for night vision).

There are two ways to define any color using only three primary colors (C1,C2,C3):
  • additive color method with RGB coding: a mixture of Red Green and Blue is added to blacK K(0,0,0)   Lighting a black video screen.
    example: hexadecimal RGB coding of the orange   (1, 0.6, 0) = (255, 153, 0) = #ff9900
  • subtractive color method with CMY coding: a mixture of cyan, Magenta and Yellow is subtracted from White W(1,1,1)   Painting on a white sheet.

Remark:  R+C = G+M = B+Y = 1  thus it is easy to switch between the two coding methods (the mixture of two of the three fundamental colors is the complementary color to the third fundamental color).
Exchanging the codings  RGB  and  CMY  exchanges the image and its "negative", thus also black and white (see the cube at the bottom of the page).
 
A color can also be defined with its hue, its saturation and its brightness (HSB coding).

RGB-CMY

RGB coding (ColorSurf by Martin Kornig)

only the hexa values 00 33 66 99 CC and FF are recommended on the web pages

RGB-CMY and HSB coding (Martin Kraus)

Each square is colored according to its position: the coordinates are translated into the intensity of the Red Green Blue component for one face and into the Cyan Magenta Yellow component for the other face; the two faces of a square are thus "negative" one from the other. Each sphere is colored with the HSB coding: its position angle determines the Hue, its distance from the axis the Saturation and its height the Brightness of the color.

references: •  color's theory by Xavier Hubaut (in French)
•  RGB code: table 1, table 2
•  Q'est-ce qu'est une couleur ? youtube video in French (science √©tonnante, 15mn)


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convex polyhedra - non convex polyhedra - interesting polyhedra - related subjects May 2004
updated 24-06-2021