There are usually three tones in black and white photos.

Although alto has no strong artistic appeal in timbre, it is more free in the expression of various themes and contents; Moreover, the three-dimensional sense of the picture is relatively strong, which is why a large number of photos are in the middle tone. High-profile photos can give people the feeling of lightness, purity, beauty, liveliness, comeliness, tranquility, elegance and comfort. They are often used to express bright and beautiful scenery, light-colored still lives, animals and so on. In portrait photography, they are used to show children, girls, doctors and so on. Low-key photos can give people a mysterious, solemn, melancholy, implicit, deep, steady, bold and stubborn feeling. The contrast between alto is strong, which often gives people a feeling of anger, strength and excitement; The contrast is dull, which often gives people a feeling of desolation, depression and simplicity.

For photographic works, "hue" is also called the hue or hue of photos. Refers to the relationship between the brightness level of the picture, the contrast between reality and reality, and the hue brightness of the color. Through these relationships, the viewer feels the flow and change of light. Tone is the style and main feeling of photos.