| Résumé : |
The colour wheel or colour circle is the basic tool for combining colours and has 12 colours based on the RYB model. Three primary colours namely Red, yellow and blue (RYB). Secondary colours are obtained by mixing primary colours, Orange, green and violet. Six more colours are obtained by mixing primary and secondary colours. Hue distinguishes one colour from another and is described using common colour names such as green, blue, red, yellow. Value refers to the lightness or darkness of a colour. It defines a colour in terms of how close it is to white or black. Chroma is the attribute that expresses the purity of a colour. When any hue is missed with black you get shade. A tint is any hue which is missed with white. When hue is mixed with both white and black, one get tone. It is degree to which the colour resembles to its hue. Colours which reflects light with mixtures of similar wavelength, the colour obtained is bright. Additive colour, or "additive mixing", is a property of a colour model that predicts the appearance of colours made by coincident component lights. The combination of two of the common three additive primary colours in equal proportions produces an additive secondary colour- cyan, magenta or yellow. Additive colour theory often used in theatrical lighting for plays, concerts, circus shows, and night clubs. Subtracting colouring uses dyes, inks, pigments, or filters to absorb some wavelengths of light and not others. The colour that a surface displays comes from the parts of the visible spectrum that are not absorbed and therefore remain visible. Measurement of colour is known as colorimetry. Variety of instruments are used to find colour properties. To measure colour value the source of light and viewing angle is very important. Tristimulus system, a system for visually match ing a colour under standardized conditions against the three primary colours-red, green and blue. X, Y, and Z are called tristimulus values. These values specify not only colour but also visually perceived reflectance. Commission Internationale d'Éclairage (CIE) in 1931, the chromaticity diagram is obtained by plotting these tristimulus values. For the rapid visual determination of the colour of objects, a colour atlas such as the Munsell book of colour is often used. The CIELAB colour space (also known as CIE L*a*b*. The Hunter Lab color space, defined in 1948 by Richard S Hunter, is another colour space sometimes referred to as "Lab". For the object with opacity greater than 75%, The Kubelka — Munk equation defines the relationship between spectral reflectance (%R), absorption (K) and scattering (S). Shades are compared using above techniques in paints, plastics chips, textile fabric. If one or more types of a person's colour-sensing cones are missing or less responsive than normal to incoming light, that person can distinguish fewer colours and is said to be colour deficient |
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Colour physics in PAINTINDIA, Vol. LXX, N° 10 (10/2020)
