The metamerism is often presented like the phenomenon by which two surfaces, appearing of the same Couleur under some lighting or Illuminating, can appear different colors under another lighting. They are in fact a consequence the human vision the colors. Just as in chemistry one qualifies made up métamères two organics isomer having even function, in the same way in Colorimétrie this word relates to two lights with the different colors according to physics but indistinguishable with the human eye.

In physics, a light is interpreted like an electromagnetic wave containing, of unspecified number with unspecified intensities, wavelengths ranging between roughly 400 and 700 nanometers (billionth of meters). This interval corresponds to the various colors of the rainbow between the purple one and the red or, more precisely, to the colors of decomposition of the white light by the prism. A wavelength thus characterizes a pure color (a color in the system TSV), all the other colors being obtained by superposition of pure colors.

In addition, the human brain distinguishes the colors through receivers called cones. It is that there exists in all and for all three types of cones, which means that any color is characterized by three parameters only, the intensities “measured” by the three cones or of the numbers which result some directly. These three types react particularly to the red, the green and blue, which results in interpreting the colors like superpositions of these three primary educations (system RVB). This system contains much less subjective colors than there are objective colors in physics.

The physical colors, infinite number, associated with only one visible color given are known as métamères. There is no reason so that two such colors remain identical after reflection on a given object, the Courbe of reflectance of this one transforming them into two colors which are not any more métamères. Category: Colorimetry

The phenomenon is also applicable when, under same lighting, the object is seen through two types of different receivers. For example, the human eye and its receivers characteristic on a side, and a camera numerical - or silver - other.

The sensors colors of the camera do not have the same spectrum of sensibilté as the cones of the eyes. It results from it that certain flowers can appear pink with the eye and mauves on a photograph.

This phenomenon is more particularly observable on the bodies containing of the organic dyes (dyes containing nitrogen, often, and thus the flowers, insects…)

To measure the metamerism, one raises the spectrum of the object under two specific lightings well defined. If the curves cross more twice, it is admitted that the surface observed present of the metamerism.