Basic knowledge of color theory (2)

Second, the human visual color system

The color is mainly generated because the human eye receives reflection or transmission from the surface or inside of the object to the light source. Therefore, the color is covered by three major factors such as light, object characteristics and human visual mechanism. In the previous article, the light source was irradiated. The role of objects has been described, but in this article, we will explain how the color of the object is reflected after the light reflected or transmitted by the object enters the human visual system.

The eyes are the windows of the soul, playing the role of evaluation, watching, and judgment. However, how does the eye accept the reflection (transmission) or the light of the external objects, and make people feel the feeling of color? First of all, we need to understand that the electromagnetic wave that can actually produce a color sensation on the human eye's visual system is a visible light wave with a wavelength range of about 380 to 780 nm. However, in this visible spectrum, electromagnetic waves of different wavelengths can produce different colors. Feeling, and the color of nature is hundreds of millions of colors, then how does the human eye's visual system recognize the color stimulus generated by the light reflected or transmitted by the object? The main reason lies in the photoreceptor cells in the human eye's visual system. The results of the action of rod cells and cone cells are described below for the visual characteristics of the above mentioned photoreceptor cells:

Rod cell

The rod cells only work under dark conditions. Their brightness is below 0.01 nits. They belong to cells with high sensitivity and low resolution. They can only recognize changes in light and shade, and have no sensory effect on color. The rod cells are only light and dark for light perception. The sensitivity range is 400~600nm.

2. Cone cells

Since cone cells do not function under weak light, it is a low-sensitivity cell, suitable for daytime vision; but when the light reaches a bright light condition of a few nits, the cones are able to resolve The details of colors and objects are low-sensitivity, high-resolution cells. Cone cells contain three different types of color-sensing cells, which are the long-wavelength, red-colored light (cones, mid-wavelength green light--cones and short-wavelength blue light--). Cone cells, so the cones can distinguish colors, and their sensitivity ranges from 400 to 700 nm.The peak sensitivity of the three different types of color-sensing cells to the spectral wavelength is located in the blue color range of the visible spectrum, respectively. 420nm, green light - 530nm and yellow-green light - 560nm, the number of three different types of color cells on the retina is approximately ρ: γ: β = 40:20:1.

Therefore, through the above explanations, we can understand that the main reason that the human eye perceives color is due to the overlapping spectra of three different kinds of color cells on the retina, so that each wavelength in the visible spectrum has The only absorption rate, the absorption rate of these three types of cone cells, the human eye's visual system can distinguish the color of the object. In addition, because the human eye has three different types of cone cells, the “three-cimponent or trichromatic theory” that has dominated the color science for many years has been developed in color vision theory. The "Three Colors of Vision Colors" will be explained in the next color technology article.

(to be continued)