Principles of addition and subtraction

The principles of addition and subtraction are as follows:

Addition is the principle of light source synthesizing light. The display screen is a light source, which can emit red, green and blue light. By adjusting the intensity of red, green and blue, others are synthesized.

Subtraction is the principle of reflecting light on the surface of an object. Some objects can reflect all wavelengths of light, such as white paper, so we see that the drawing paper is white; The pigments used in painting can only reflect some wavelengths of light, red pigments reflect red light, and the rest of the light is absorbed (subtracted) by pigments, so we only see red.

Schematic diagram of addition principle. There are three kinds of light sources: red, green and blue. We set (0,0,0) in photoshop, which is equivalent to telling the display screen to turn off the red, green and blue three-light area of this pixel, and then we see a black dot on the screen. And (255, 255, 255) is equivalent to maximizing the brightness of the three light areas, so the center presents a white point.

Subtraction is just the opposite. Originally, drawing paper could reflect all colors. Later, we painted a pigment with a brush, which only reflected one color, and all other colors of light were absorbed by it.

Because pink pigment absorbs all light except pink, cyan pigment absorbs all light except cyan, and yellow pigment absorbs all light except yellow, all colors are absorbed in the overlapping area of the three pigments, and we can only see black.

The simplest addition:

The simplest addition is that when two colored lights hit the same point, a new colored light will be formed, but the color of the new colored light is very easy to calculate. For any linear color coordinate system (such as CIE XYZ system), it is only necessary to add the coordinates of the original two color lights (plus the position vector) respectively.