Outline Drawing
The rendering of any form in outline is probably the simplest form of convention, which is generally accepted through tradition as representation. Though the objects so depicted really depend on light, shade, and local colour for their appearance.
Such outline drawings may be in other respects realistic, but a further degree of convention is the desirable elimination of perspective where it is unsuitable to the effect desired. For instance, in silhouette, profile renderings only are intelligible, and in delicate bas-relief modelling any foreshortening should be avoided if confusing to the effect.
In direct personal work, such as drawing or painting, when craft conditions other than that of the medium employed are not involved, convention is purely a matter of discretion and consideration of the nature and object of the work; but it is essential in design when the material and method of production have to be considered. In painting the artist may employ the full resources of his palette and be as realistic in his effect as is in his power, but if the purpose be mural decoration restraint is at once imposed.