I.D - Color reproduction¶

When it is a question of reproducing (synthesizing) colors, two systems are possible, according to the fact that the device is “passive” or reflecting (in painting, printing, etc.), i.e. that it needs to be illuminated, or “active”, and emits its own light (screen, projector, etc)

D.1 - Additive synthesis¶

When a system emits its own light, such as a screen or projector, it produces colors ranging from black* (a system that is turned off, emitting nothing), to white*.

In such an additive system, the most luminous color is the white: it results from the addition of the various primitives * of which the pixels of the device are made, in general a combination of green, red and blue.

This system works by adding rays of light to mix the colors.

A consequence to such a system is that a monochromatic color (the color of a primary* of the system, or the simulation of another monochromatic light obtained by mixing these primaries*) is inevitably less intense than a white one, contrary to the real world where everything is possible.

An additive system, being a light generator, can work in complete darkness, in which case the color reproduction can be perfectly controlled by not being influenced by any external light (as in a movie theater).

D.2 - Subtractive synthesis¶

When a color reproduction system is a reflective surface, it is the pigments that alter the light received; each pigment absorbs part of the rays received and reflects the rest. The resulting light is therefore necessarily of a lower intensity than that illuminating the surface: the system subtracts light rays from an available bouquet.

Such a subtractive system thus produces the colors by going from white* (reflecting all received light) to black* (absorbing all received light).

An important consequence is that a subtractive system depends on the light that illuminates it to reproduce colors: seen under a light poor in monochromatic rays*, an exposed painting will not render all its colors possible. For that, it is necessary to illuminate it not only with a white light, but with a white light “containing” enough different monochromatic* rays, of high quality¹.

A painting, a poster or any other object illuminated under a monochromatic light will be able to reproduce only this monochromatic* color, at different intensities, whatever the pigments which compose them.

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