Concepts of hue, lightness and saturation in photography

The three basic concepts to describe color are hue, saturation and lightness. Roughly speaking, hue defines a certain color: this color is red, blue, green, purple or yellow; Saturation defines the purity of this color, that is, how many other colors are mixed. The more other colors, the lower the saturation of this color. Brightness defines the brightness of a color, that is, the brightness of a color.

The photography teaching webpage/tutorials/color-perception.htm explains the concepts of hue and saturation from a physical point of view, which is very clear:

Physically speaking, light is electromagnetic wave, and the color of light is the frequency of electromagnetic wave. All the colors we see correspond to a certain frequency range. Tone refers to the frequency or color corresponding to the peak of electromagnetic spectrum. If the peak of the electromagnetic spectrum is in the green position, the hue of this light is green; If the peak is in the yellow position, the hue of the light is yellow. That is, the hue corresponds to the peak position of the electromagnetic spectrum. draw

Saturation, that is, the purity of color, corresponds to the width of electromagnetic wave peak. The wider the peak, the worse the color purity and the lower the saturation. The narrower the peak, the better the color purity and the higher the saturation. draw

The article doesn't talk about the lightness of color. We know that lightness describes the brightness of a color, that is, the corresponding electromagnetic wave intensity, so lightness should correspond to the peak height of electromagnetic wave. The higher the peak value, the brighter the corresponding light and the greater the brightness.