An artist drawing, for instance, may choose to draw from what he or she observes in front of them, or from what they imagine or from what they already know about the subject. These 3 methods will, very probably, produce 3 very different pictures. A careful methodology would include an examination of the materials and tools used and how a different type of canvas/brush/paper/pencil/rag/camera/chisel etc. would produce a different effect.
