Operational definition of sketch: a painting that expresses brightness change with a single color. According to certain painting principles, painting tools and artistic activities that intentionally shape objects on the screen carrier. Sketch is a variant of sketch. Sketch level is one of the important indicators to reflect the painter's spatial modeling ability.

Features:

Sketch is a kind of monochrome painting, using charcoal pen, pencil, pen and so on. Used to draw light and dark objects with lines. Monochrome watercolors and monochromatic oil paintings can also be counted as sketches; China's traditional line drawing and ink painting can also be called sketch. Generally speaking, sketch diversification refers to pencil drawing and charcoal drawing. Sketch is the foundation of all painting, and it is a necessary stage to learn painting art.

Sketch usually uses methods that can leave traces on the plane: such as charcoal pen, pen, brush, ink, paper and so on. Outlines and lines are general terms for sketches. Sketch has a feeling of natural law. Different strokes create different lines, intersecting relationships and rhythms, active and passive surroundings, planes, volumes, tones and textures.