Image And Color – The Basis

It is known that color derives from light. The planet is illuminated by light waves emitted by the sun, differentiated in wavelength, giving rise to various colors, which, when seen together, form the color white. The characteristic popular phenomenon demonstrating this reality is the formation of rainbows on rainy days, because water represents a medium with a different optical density than the surrounding air, and light waves refract when they cross the boundary from one medium to another. By refracting white light, the millions of tiny water droplets cause the perception of the constituent colors of light, like a separation of colors. This phenomenon is observable in many circumstances, between air and water or any other transparent medium of different density, because only transparent materials allow the possibility of refracting all the colors of the visible spectrum contained in white light. Opaque surfaces and objects absorb some of the colors contained in white light and reflect only a few, depending on the properties of the object. When, for example, one observes an orange, only wavelengths between 590 and 625 nanometers are reflected, with all others being absorbed by the object itself – hence, when looking at an orange, one only sees orange tones because these are the only ones it reflects.

The interest in the human optical mechanism lies in the basis of color formation, studied in almost all arts, through two distinct processes – additive and subtractive. The additive process is precisely that proposed by the human eye, and which occurs in the retina. The retina is a peripheral layer consisting of a complex and sophisticated system of nerve components and photoreceptors, among which are the so-called cones and rods. Cones are responsible for color information (high level of luminosity) and rods for black or gray information (low level of luminosity). There are three types of cones, with three different sensitivities, corresponding to the three wavelengths of light – long, medium, and short. This distinction involves the three primary colors of the spectrum – red (long wave), green (medium wave), and blue (short wave). This process is called additive because the primary colors are added in various combinations to produce a much wider color spectrum, depending on the intensity of the light. When the intensity is zero, each of these colors will be perceived as black, and when the intensity is total, each of these colors will be perceived as white. This is the so-called RGB color system, also characteristic of the digital world, capable of generating nearly 17 million distinct colors (on a generic basis), of which it is commonly said that the human brain only distinguishes between 2 and 10 million, depending on the optical anatomy of each individual.

The subtractive process is the opposite of the additive one; it was created for the material world and is therefore considerably more limited in the number of distinct colors generated – about 16,000 (on a generic basis). The additive process originates from light, and the subtractive process originates from inks and materials. Unlike the RGB color system, the subtractive mode is a model in which the ink reduces the light that would normally be reflected. While in the additive mode the mixture of colors channels to total light – white – in the subtractive mode the mixture of colors absorbs light until the total absence of light – black. The subtractive method is based on sets of colors used to generate other colors, which are called primary color sets. Colors are defined as such when no other color can generate them, but within the limitation of a specific model, such as the RYB model [Red (R) Yellow (Y) Blue (B)] – more common in Fine Arts – and the CMY model [Cyan (C) Magenta (M) Yellow (Y)] – more common in Graphic Arts.

However, the primary color system is not restricted to the concept of origin, and can be extended to systems for the mere obtaining of secondary colors through sets defined by personal choice, as happens in the screen printing technique by simulated color selections (p. 305) and in other image reproduction techniques. In a subtractive color system, other essential aspects of color are also studied – such as hue, lightness, and saturation – which then expand to other properties important to the combination of colors (harmony) – such as temperature, contrast, proportionality, rhythm, complementarity, and tension – perspectives that are widely developed in an artistic context and briefly mentioned in this post.

The subject of color, in whatever system, also involves an immense variety of perspectives, among which theories based on cognitive and psychological analyses of the color perception mechanism operated between the human eye and the brain intersect, since color is not a tangible phenomenon of Physics, but part of a complex interpretative psychic process that has made Colorimetry a vast science, still undecipherable in numerous aspects, despite centuries of study.

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