Non-Photorealistic Rendering: a Brief Introduction


The purpose of this page is to provide a brief overview of non-photorealistic rendering or NPR, with one example that enhances the quality of a photograph by adding artistic effects.

NPR and its predecessor, photorealism, are briefly introduced below. For more information on these terms, please follow the hyperlinks given in the section titles below. The linked resources contain extensive documentation on both topics.

Photorealism Defined

To understand NPR, briefly consider its predecessor movement - opposite movement, if you will - called photorealism. Photorealism was popular in 1960-1970. Photorealists transferred images from photographs to canvas, using mechanical or other means to maximize fidelity to the original image. But the new version of the image was rendered in traditional media such as oil on canvas, often many times larger than the original.

Today, the discipline of computer graphics employs an extensive set of photorealistic, and as we shall see, non-photorealistic techniques.

Rapids as shot
Figure 1. As Shot.

NPR Defined

NPR refers to the use of the techniques of computer graphics to enhance an image, to make it more interesting and heighten its aesthetic qualities. Examples include computer-graphic simulation of watercolor, palette knife and pencil drawings. Many other techniques are available. The intensity and degree of detail can be varied by means of controls presented within the graphical interface to each technique. The manner of employment, the selection of different combinations of NPR techniques, as well as the very order in which they are applied, are endlessly variable, and in the end, limited only by the user's creativity and imagination.

Rapids NPR
Figure 2. NPR Applied to the Image of Figure 1.

NPR Application Example

The effectiveness of NPR techniques is illustrated with one example consisting of the three images shown at right. Figure 1 shows the image as shot and downloaded from the camera. Figure 2 shows the same image with NPR techniques applied. NPR is employed to create a more pleasing, artistic rendition of the original photograph. The effect is like that of watercolor or oil on canvas as might be rendered by an artist painting the scene from life, in this case the rapids of a flowing river.

Because the image is small, the viewer may have difficulty discerning the effect of the NPR techniques applied. Electronic display of a full size image would be impractical in most cases. Figure 3 shows a full-size vignette, a portion of the NPR image as it would appear in full size. A number of other vignettes may be found on this site.

Viewer Feedback Requested

Please send your feedback. Adoption of NPR is comparatively recent, as is this attempt at description and illustration of the process. I would appreciate any comments as to effectiveness of this page and how it might be improved.


NPR Full Size Vignette
Figure 3. Full-Size Vignette Showing NPR Effects.

Reference: Hayes, Brian, Computational Photography. March-April, 2008. American Scientist v. 96, No. 2, p. 94.