When an artist has completely prepared their canvas, the next step is to lightly draw an outline of the work they will create. This step is not mandatory, but it does assist the artist with the fine details of their work. Painting is a two-dimensional form of art that is made to look as if there are three dimensions. Drawing in the outline gives the artist a chance to ensure they are using the correct perspective before they ever add a stroke of paint.
Adding depth to a painting gives it a more modern look. Primitive artists that used pigments on their work often left out perspective. It was simply not something they learned because it had not yet been discovered as a necessary form for realism. After artists learned how to create depth with perspective, the nature of painting changed. While it remained a two-dimensional form of art, the finished product was expected to look like it had depth.
Artists today often find that doing a vague outline is the best way to get their perspective correct. They can use color and tone to show this in the final painting, but the sizes of objects must be proportional for it to be believable. Using drawn outlines helps artists with spacing and size when they paint. A vase that is far away must be small enough for the perspective to be correct. If it is too large, the artist will have to do their painting again.
There are few shortcuts when creating a painting. One that utilizes a perception point to create depth is time-consuming. Drawing out the major figures in pencil or charcoal helps the artist to judge the correct size and spacing before painting begins. Once done, they will not have to worry about going back and recreating their work to get the correct perspective.