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The subtractive synthesis is the operation consisting in combining the effect of absorption of several colors in order to obtain a news from it. For example, the superposition on a white surface of two filter S coloured, one yellow and other blue, makes it possible to obtain green

The subtractive term comes owing to the fact that a coloured object withdrawn (absorbs) part of the incidental light. In fact, a color obtained by subtractive synthesis several others will be necessarily darker than they.

In subtractive synthesis, the primary Couleurs generally used are three: the Cyan, the Yellow and the magenta

the addition of these three colors gives Noir
the absence of color is the Blanc (if the support is white)
the addition two to two of these primary colors makes it possible to obtain the secondary Couleurs:

the cyan and the yellow give the Vert
the cyan and the magenta gives the Bleu (blue-purple)
the yellow and the magenta gives the red (red vermilion)

The subtractive synthesis is the principle which regent the mixture of pigments coloured in painting, printing works and paper impression for photography color.

In theory the use of the three primary colors makes it possible to reproduce all the existing colors. However in Imprimerie one adds the black to the three primary colors for several reasons:

mainly because three primary inks (three-color process) do not allow obtaining a neutral and major black. Indeed the pigments of primary inks are not rigorously primary (especially the magenta) and their transparency is unequal (problem of superposition).
also because the file of the black carried out with a strong contrast makes it possible to increase returned details of the image and blacks major.
finally to save primary inks (more expensive) black ink allows advantageously in tons black and the tertiary colors dark and désaturées to replace them by a special treatment called " withdrawal of under-couleurs" or better by the " stabilization of the gris" more complex and which requires the use of an adapted software.

Contrary, when an illustration envisages in a quadrichromy to place a stringcourse of black flat tint, one generally applies a quantity of the primary educations (or only of the cyan) under the black to make it more powerful.

The subtractive synthesis also applies to the apparent color of the objects. Thus the color of an object depends on the color of the light which it receives and of the physical and chemical nature of this object. Each object can absorb or reflect the light which it receives.

To illustrate that with some simple examples:

An object appears white if the light that it receives is white and if it reflects the totality of the primary components of this white light (red + green + blue) (see additive Synthèse). It will be black if it absorbs the three components entirely.

An object consequently clarified light will appear red if it absorbs blue and the green and reflects the red. It will appear yellow if it absorbs blue and reflects the red and the green, etc the other colors are caused by variable proportions of reflection and absorption.

To finish, our object which appeared red under a white light, lit by a red beam will be always red then that it reflects the red and nothing has to absorb. If one lights it with a beam green or blue it absorbs all and can nothing reflect: it will appear black.

This makes it possible to understand that the natural light (sun) not being perfectly white and in addition varying at the various times of the year and the day the apparent colors of the objects change: snow will take different tonalities for example.

This well-known phenomenon in Photography and video calls with a permanent correction: it is the adjustment of the Balance of the white.

See too

External bond

the colors

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