A bit of physics and Biology: The 3 characteristics of color

Brightness

If we see an object, it is thanks to the light which leaves from this object and reaches our eye. Without light, we see nothing. This light can be emitted by the object itself (this is the case of the filament of a bulb, the sun and the stars for example), or else reflected (the moon for example is visible only because it is lit by the sun, and most of the objects that surround our daily life do not emit light either, but we see them thanks to the light they reflect).

A light color has a greater brightness than a dark color. The brightness of a color therefore corresponds to the amount of white light reflected by that color. If all the white light is reflected, the object will be white, whereas if it does not reflect any light, it will be black. The difficulty in appreciating the luminosity of a color is to manage to disregard its saturation and its hue. Biologically, within our eye, the cells that are specialized in the perception of light are called rods.

Hue

The hue is governed by the dominant wavelength of the light received by our eye (therefore emitted or reflected by an object that we see). This wavelength is part of the visible spectrum (otherwise we just wouldn’t see the object in question!).

There are three of them, and they differ depending on whether we are in additive or subtractive synthesis. Specifically, additive primary colors are opposed to subtractive primary colors. The three primary colors are chosen in such a way that once superimposed on each other they give white or black (depending on whether it is additive or subtractive synthesis). For subtractive synthesis, the three primary colors are Cyan, Magenta and Yellow (CMY), while in additive synthesis they are Red, Green and Blue (RGB).

When you work on a computer, each pixel emits a color. When the pixel values ​​are at 0, the screen is black, conversely when they reach the maximum values ​​the screen is white. You are therefore in additive synthesis!
In the rest of the presentation of colors (secondary then tertiary) we will limit ourselves to additive synthesis (RGB), since you are probably reading this article from a bright screen.

Secondary colors

The secondary colors are obtained by the mixture of two primary colors, quite simply. In additive synthesis, the secondary colors are therefore Cyan, Yellow and Magenta. Do these three colors ring a bell? Normal, they correspond exactly to the three primary colors of the subtractive synthesis!

Be careful, unlike subtractive synthesis, in additive synthesis it is normal for the mixture of two colors to give a brighter color.

Tertiary colors

In an additive system, the term tertiary color can have several meanings. On the one hand, tertiary colors are obtained by mixing a primary color with a secondary color, in equal parts. They are therefore six in number, but their name in the additive system (unlike the subtractive system) is not defined. On the other hand can be considered as tertiary colors mixtures in equal parts of two secondary colors, and in this case there are three, supplemented by three quaternary colors.

Then there is the entire infinite spectrum of shades, changing the mixing ratios of each color.

Complementary colors

In additive synthesis, two colors are said to be complementary if, mixed together, give white. They say they “cancel each other out”. They are easily identifiable on the color wheel because they are opposed to each other.

Isophane colors

We call isophane colors colors having the same value, the same gray level. If the image were shades of gray, one simply could not distinguish two isophane colors, because only the hue distinguishes them. Such a choice of color can sometimes pose reading problems, and generally tend to flatten an image rather than give it depth.

Pastel colors

Pastel colors are low saturated and bright colors. These settings give colors that are qualified as soft, clear or even tender.

The different types of contrasts

Brightness contrast

This is the phenomenon that makes the same color appear darker when it is on a light background than when it is on a dark background. If you want to look tanned, dress in white! This difference in persception is due to the ability of our pupil to adapt to the brightness of an environment. In a bright environment, the pupil closes, letting in less light, making the color appear darker.

Saturation contrast

Also called “quality contrast”, this contrast emerges on the juxtaposition of colors with different degrees of saturation. We commonly speak of bright colors for saturated colors and dull colors for those that are less saturated. A color put on a dull background will appear more vivid than put on a more saturated background because our eye evaluates the saturation of a color in relation to its environment.

Color contrast

The color contrasts can play on the juxtaposition of primary shades or warm and cold shades for example. Such a contrast gives an additional tint to a color: the same orange will appear more yellow on a red background and, on the contrary, more red on a young background.

Simultaneous color contrast

The simultaneous contrast of colors is the name of a law enunciated in 1839 by the French chemist Michel-Eugène Chevreul: “The tone of two areas of color appears more different when observed juxtaposed than when observed separately, on a common neutral background “. (The “tone” of which Michel-Eugène speaks here is none other than what is also called the hue). He also published in 1889 a work entitled The Law of Simultaneous Color Contrast.