In the mid-20th century, painters were self-conscious and perhaps a little defensive about the structure and process of painting. Many artists felt that paintings should appear to be flat rather than three-dimensional, because three-dimensionality can just as easily be conveyed in sculpture or photography as in painting. Moreover, the mass production of cameras allowed three-dimensional representations of nature to be made by almost anyone. Painters of the 20th century felt that a painting should look like a painting (in other words, flat), and should also reveal the process of its own creation—it should be obviously hand-made. American painter Adolph Gottlieb (1903-1974) was one who endorsed these ideas, insisting that there should be little distinction between the foreground and background of a painting, so that the viewer's eye is compelled to scan the surface rather than be drawn to a single point of reference. He and the painter Mark Rothko published a set of artistic principles emphasizing the use of flattened forms with little or no depth of field, a concept known as “reasserting the picture plane.” (New York Times, June 13, 1943.) Gottlieb and Rothko were also adamant that pictures should express important ideas; in their view, there was no such thing as a good painting about nothing.
Cole TB. Penumbra. JAMA. 2011;305(22):2261. doi:10.1001/jama.2011.770