This drawing by Ingres is composed in a very unusual way. If this scene were before you in reality, you would observe much more visual variety in it, and if you compared the real scene to this drawing you would see that Ingres imposed a great deal of visual unity onto the subjects. For instance, the long, angled ribbon that falls from the older girl’s hat diagonally and to the right is repeated in the edge of the younger girl's coat. It's also easy to see an implied line that runs at a similar, but opposite angle behind the heads of both girls. Their feet mirror one another and the lightness of their outfits unify them. Both girls are light shapes hedged in by darker shapes. The shadows among their lighter clothing have been de-emphasized whereas the shadows have been emphasized in the darker clothing. They are also obviously wearing the same style of hat for this same reason. Perhaps another artist depicting the same subjects would have used the forms of each figure to contrast them with each other, or perhaps they would have used different forms altogether.
On another level, these formal qualities (“formal” meaning pertaining to visual form) are integrated into the paper format. The tonal variety (contrast) is roughly central in the format--the paper does not stick out three feet to the left or right, nor does it crop the figures. The paper is not shaped like a starburst, like an irregular blob, like an animal or like a thin, long strip although all of these paper shapes were available options. The composition, like the figures, is poised, balanced and calm.
These artistic decisions are some of the reasons why I do not take seriously claims by some art historians and artists (such as David Hockney and others) that artists like Ingres used optical devices to make their work. The implication being that their work is therefore over-rated because their artistry was in fact dependent upon a technical innovation instead of whatever the hell it is that artistic quality is based on. The technical feat of representational drawing is itself, merely a means to a greater end and it makes no difference if the artist used a drawing-grid, a camera obscura, a camera lucida, a camera, tracing paper, an assistant or even a highly advanced robot to accomplish the technical tasks of creating a work of art. If a work fails to serve the function of art, no amount of technical achievement can help it. If a draftsman does not know (at any level) what the purpose of a work of art is, no technical innovation can make it for him.
The “optical device” claim reminds me very strongly of when I was a child and my classmates and I thought drawing with a ruler was “cheating.”