The main difference between these two kinds of knowledge is that art doesn't require two or more people to agree about what they've seen before an observation is published. The artist publishes his observations when he alone decides that these observations are correct. Learning to become an artist is to learn how to value one's own observations of the world, how to make those observations fully and accurately, and how to communicate those observations to others. This essay is limited to three things the graphic artist creates. Portraits, Landscapes, and Still Lifes.
Portrait painting limits the artist's compositional skills.
A background is glimpsed at the edges of the painting. The famous Mona Lisa has an interesting problem in the background. Landscape painting also places constraints on the artist's compositional skills. Half sky and half earth. This is one case where the camera doesn't help at all, since the light intensity is rarely the same on both halves of the plate.