Simulating the perception of the colors of organic colorants

Colorants are widely used in the chemical industry (for research into new shades, tonal fastness, etc.) to enhance the aesthetic qualities of plastics and provide good protection against ultra-violet rays. In the automotive industry, pigments are of mineral or organic origin and insoluble. Depending on their nature, they confer anti-corrosion, opacity and sealing properties to paintwork. In addition, all non-allergenic colorants are used in the cosmetics industry. They also have numerous applications in the textile, printing, art, food and construction industries.

Color is first and foremost a perception. It is therefore excessive to think that matter has an intrinsic color. Indeed, a textile that appears red in daylight can be black in green light, because it absorbs all light except that of high wavelength. It follows from this preliminary observation that we need to define color more precisely. Light is produced by an illuminant and then interacts with matter, the object. Finally, a certain quantity of light is perceived by the observer, which the eye breaks down into three electrical signals sent to the brain. It is the brain that creates the sensation of color. Physiological perception is linked to three parameters:

• the nature of the illuminated object ;

• the light that illuminates the object (the illuminant). A light source is also referred to as a primary illuminant, while a surface diffusing or reflecting light is called a secondary illuminant;

• the sensor (the eye), which receives the message and communicates it to the brain via electrical impulses. Remember that color is nothing more than the eye's perception of a spectral distribution R (λ). It's important to note that the eye can't tell the difference between, say, a monochromatic yellow and a mixture of equal amounts of red and green. This property enables what is known as trichromatic synthesis, which is the basis of all colorimetry (additive synthesis). Color is therefore a stimulus that is conventionally reconstituted by three primaries: red (700.0 nm source), green (546.1 nm source) and blue (435.8 nm).

It is therefore interesting to quantify the color of a dye by calculating its absorption spectrum. Various colorimetric models involving the dye's absorption spectrum, the spectral density of the illuminant and the reflection of the substrate are thus implemented. The following section presents software and a model for simulating absorption, transmission, reflection and perception by the human eye. The quality of the program has been tested in a number of academic cases, and the influence of each of the program parameters on the simulated trichromatic values has been studied....