Thanks for the comment. Paintings are a very interesting case, but I do not consider them to be abstractions. If we render a tree with a computer, we need to abstract and define all components of the tree: trunk, branches, leaves. Rendered image is then derived from information about each component (their spatial dimensions and position).

In the process of painting the artist usually draws a picture without abstracting or naming things. He paints a tree as a whole as he sees and feels it, without consciously distinguishing parts. On the other hand, technical or instructional drawings could be considered visual abstractions.