Line drawings are visual images where the edges, contours, and important features of the objects being represented are depicted with lines, which can optionally vary in width, juxtaposition, and density to produce spatial and tonal effects.
In recent years, line drawings have begun to suffer from a “bad rap”: in the age of the internet—where the disincentives to publication of full colour images have mostly disappeared—some people seem to think that line drawings are somehow “second best”. When publishing full-colour tonal images costs no more than a line drawing, doesn't it always make sense to use full-colour imagery?
A short answer: No. Line drawings excel at certain tasks, and are often easier for people to interpret than tonal representations or photographs. Early seminal work in this area includes a study by Ryan and Schwartz 1) who found that subjects perceived carefully prepared line drawings of familiar objects faster than grayscale photographs. It is also very common for documents like instruction manuals to be illustrated with line drawings.
There is also perhaps a feeling that line drawings are somehow easier than tonal illustrations. While they can often be simpler, high-quality line drawings are very difficult to create. There are many qualities of even simple line drawings that can affect their interpretability:
There is a reasonably large research literature on the perception and efficacy of linear depiction. Unfortunately, much of the educational literature on the usefulness of line drawings (and visual media in general) suffers from poor control of the quality of the evaluated stimuli. More recent research from the vision and computer sciences is usually far more reasonable in quality of drawing. Line drawings have been shown to excel at the following tasks:
Line drawings are less suitable in contexts where the detailed representation of tonal variation or texture are required. Even so, highly skilled illustrators can represent tone and texture in line by using techniques such as eyelashing, cross-hatching, and stippling.
Conrad Taylor has a good paper 2) on the meaning of line thickness in technical drawing. In recent years, Non-photorealistic rendering (or NPR), has become a very active area of computer graphics research. Advocates of NPR, which often has a line-drawn appearance, emphasize that photorealistic rendering is often unsuitable or undesirable in many contexts.
Here is a brief history of technicial illustration that seems to show a progresson from form to line. Interesting. And this is the website for ITEDO Software. It provides a gallery, tips and tricks, literature and links on technical illustration topics.
And from the above page I came across a UofT alumnus David Kirsch now at the University of California, San Diego, via Oxford and MIT. Timely publications. Our multimedia education friend Richard E. Mayer is in the area, at UC Santa Barbara.
For those interested in a very specific application of line drawing in the documentation of scientific data, Dominic Lopes has written an article on the illustration of stone tools: “Drawing in the Social Sciences: Lithic Illustration” . The very precise rules imposed on the illustrator of stone tools speak to the importance of conformity to convention in scientific illustration. David Van Reybrouck has elaborated on this subject in a very compelling article: Imaging and imagining the Neanderthal: the role of technical drawings in archaeology 3).
Approaches to line drawing vary. In surgical illustration, where pen and ink is popular, a style has emerged that has become the convention. The principles of this style are beautifully summarized in this document prepared by Gerald Hodge.