Color article 07

Strictly speaking, I am not a person who knows colors at all, let alone a person who lives by "fiddling with colors". But I still want to talk about a topic about color, which sounds a bit professional. Namely "additive mode" and "subtractive mode". Understanding these two concepts can not only deepen our understanding of the color world, but also help to improve the level of photoshop. As I am not a professional, I will explain these concepts from a popular point of view.

We generally know that color is the visual effect of human eyes on visible light with different wavelengths (hereinafter referred to as light, for convenience). When a certain wavelength of light enters the human eye, we see a certain color. However, the sources of light waves are different, which constitutes the basis of two modes: additive color and subtractive color.

For example, we see a red flower on the computer screen. This red light wave comes from the screen. It is the screen itself that emits light with a specific wavelength and directly enters the eyes (we don't discuss whether the light-emitting mechanism of the screen is electron rays or liquid crystal refraction). However, what we see during the day is the real safflower, but this red light wave comes from the sun. Sunlight (sunlight is a mixture of seven colors of light) shines on flowers, and only the light with red wavelength is reflected (all the colored lights with other wavelengths are absorbed by flowers). So the red we see at this time is what is left after subtracting the non-red part from the seven-color light. In fact, in an environment with external light, the color of any unlit light we see is the remaining (reflected) part after subtracting the absorbed light from the external light. The so-called "subtraction" in the subtraction mode is to subtract from the light source. In the theoretical environment, it may even produce some unimaginable effects.

For example, suppose we are in a vacuum room without light and there is a red flower in front of you. If we don't turn on the light, we won't see the flower at all. However, if a blue light shines directly on the flower, can we see the flower? What color would it be if I saw it? Theoretically, we still can't see this flower. If we can see it, it will never be red, but blue. Because red flowers will absorb blue light waves, even if they are not completely absorbed and miss a little, the reflected wavelength is still blue. There is no light source with red wavelength in the whole room, so you can't see red anyway.

For all non-illuminators, the color it presents is formed in a subtractive mode. Obviously, printed matter does not emit light, so the CMYK mode it adopts is naturally subtractive mode.

Although we understand the subtraction mode, the addition mode is not the simple opposite of the subtraction mode. When it comes to additive models, we have to mention Hammholtz and Thomas Young's trichromatic theory.

According to this theory, normal eyes have three kinds of color receptors. Each sensor is very sensitive to only a specific part of the spectrum. When they are stimulated by different wavelengths of light, they will feel different colors psychologically-red (R), green (G) and blue (B). Red, green and blue are the basic colors, and all other colors are composed of these three colors. Therefore, the "addition" in the additive color mode refers to the meaning of "addition" of ternary colors with different proportions, intensities and other factors. But the addition mode discusses the light source, not the processing state of the light source after passing through some objects. So RGB mode is called addition mode.

If we put additive color and subtractive color together, we will understand that they are not simple opposing concepts. Additive color is the addition of ternary tones, and subtractive color is the subtraction of light sources. Moreover, in fact, any light source is also an "addition" of three colors.