Colour primary

White light can be thought of as a combination of three primary colours red, green and blue. 

White light is composed of the additive primary colours of red, green and blue. These primary colours are the ones which cannot be made by mixing any of the other two together. Mixing light of two of these primary colours in equal proportions produces the following colours ... 

Subtractive colour mixing is used for dyes and pigments where the primary colours are red, yellow and blue. 

The Greek philosophers coupled a four-element theory to the idea of four primary colours to Empedocles these were white, black, red, and the vaguely defined ochron, consistent with the preference of the classical Greek painters for a four-colour palette of white, black, red, and yellow. The Athenian astrologer Antiochos in the second century ad assigned these colours, respectively, to water, earth, air, and fire. 

Pigmentation can range from "inert types, such as barium sulphate, magnesium and calcium silicates together with a primary coloured pigment such as iron oxide, to anticorrosive pigments such as red lead, zinc chromate, zinc or calcium phosphate, etc. Others, which may be included to... 

Numerous white OLEDs have been fabricated (Kido et al 1994, 19%, Dodabalapur et al 1994, Yang et al 1997). In the fabrication of full colour display all three primary colours have equal importance but white light emission has drawn particular attention because any desired colour range can be achieved by filtering of white light (Strukeji et al 19%, Zhang et... 

In a tristimulus colorimeter, three or four filters duplicate the response of the standard observer. The filters, which correspond to the three primary colours in the spectrum (red, green and blue), can be combined to match most colours. The more sophisticated instruments carry a fourth filter to simulate the blue part of the CIE [[X bar]] function shown in Fig. 5.1. The other essential parts of a tristimulus colorimeter are a white light source, an array of photometers and, nowadays, a computer or an interface to one, as shown in Fig. 5.2a. The computer can collect responses as well as carry out data transformations between CIE and other colour scale systems or between different standard white light sources or white diffusers. Hunter and Harold (1987) give a good summary of the transformation formulae employed. Data from a colorimeter is given as a three-point output, commonly CIELAB, HunterLab or 7, x, y. 

Dielectric colour-separating mirrors made of extremely hard and chemically resistant oxide multilayer films enable nearly losss-free separation or mixture of the primary colours. Such colour splitters can be made for different spectral ranges of the reflection band, broadband and narrowband. Fig. 16 shows an example of a red reflector at 45° incidence. 

Another application for colour separators is film printing. In this case, the primary colours are separated by means of mirrors, which produce three colour channels. Apertures mounted in each channel then provide continuous regulation of the light intensity for proper colour balance and production, as shown in Fig. 19. Poor quality colour film copies sometimes result from the overlapping sensitivity ranges... 

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