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Non-Photorealistic Rendering

Vol.32 No.1 February 1999
ACM SIGGRAPH

Personal Thoughts on Non-Photorealistic Rendering



Doug Cooper

Most of the non-photorealistic rendering (NPR) work that I’ve seen is in the feature animation industry, and a lot of it centers around “toon-shading,” or the rendering of 3D objects to match the look of traditionally drawn 2D artwork. To some, it may seem like this is NPR’s only current application area.

As in many industries, computers came into film as a tool to automate; to make production faster and more efficient. Computer graphics (CG) has been used successfully in feature animation to improve production efficiency in many areas, such as digital ink and paint. It has also helped free the artist from constraints of the physical world — allowing for an unlimited number of layers in a given scene, or freeing the camera to move in ways more dramatic than possible with a physical animation camera.

By using “toon-shading,” a form of non-photorealistic rendering, to render 3D objects, we’ve achieved a marriage between CG images and traditionally drawn art that allows us to create more complex props and objects. We can also create scenes with thousands of characters that would be far too complex or costly to draw. We use these tools because they produce a look that is “good enough,” and that relates in style and design to traditionally hand drawn art. Using the computer for these images allows us to create things in volume and at a scale that would be otherwise impossible.

Yet as the tools and technology grow, I feel there is much more potential for non-photorealistic rendering techniques than merely the ability to make films faster and cheaper, or to reproduce the look of other artistic mediums.

When comparing CG effects that mimic traditional art, to the real thing, I think that if you want the best quality art it is better to do things the “old fashioned” way. Drawings look best when drawn, encompassing all of the expression and nuance of the artist, not technically drafted by a computer. Computers are very good at carrying out instructions, but we’re still not able to explain to them how to draw with emotion.

Doug Cooper has worked in feature animation for seven years. Starting as a Technical Director at Amblimation, he worked on the films We’re Back! and Balto. Most recently, he completed production on the Red Sea sequence of DreamWorks Animation’s Prince of Egypt as a Digital Effects Animator. Cooper is currently the Digital Effects Supervisor on DreamWorks’ upcoming film, Spirit of the West. He can be reached via email at dougc@pobox.com.

The copyright of articles and images printed remains with the author unless otherwise indicated.

In contrast, we’re finally starting to see more work being done with CG to explore new visual ideas, and execute concepts that people only imagined before. I feel that there is a shift away from making the computer try and do the job of an artist, to instead using the computer as it should be used: as an artist’s tool.

In current feature animated films, we’re seeing the combination of 3D modeling, and image based rendering technologies being applied to create 3D sets, environments and effects that look and feel like paintings. These films are not only using CG in purely algorithmic ways, but also to enhance and manipulate existing artwork. This goes beyond just 3D rendering, to include the use of warping and morphing effects, and image processing techniques driven by quality artwork as a source. It is here where I feel that we are finding the greatest successes in CG and non-photorealistic rendering techniques.

Art has always helped us in interpreting our world, and in sharing our perspective with others. It is this part of the field of non-photorealistic rendering that stimulates me; not that we can make an existing art form easier to produce, but rather that we have new and different ways to relate to our world through new types of art.

We are now finding great successes in manipulating the traditional art forms, such as paintings and drawings with computer tools. Beyond that, there is much ground to explore that has the potential to open up new visual styles. As with any medium, success will come from learning how to apply the emerging techniques, feeling through their strengths and weaknesses and by opening our eyes to new ways to create — not by constraining the new medium to replicate or replace what has gone before it.

Computer graphics is the most versatile medium to ever be placed into the hands of visual artists. I challenge us all to find new ways to make use of this new medium.