ainting by computer can be cool. But some artists are more interested in brush strokes than mouse clicks. They like the feel of the brush pushing paint around the canvas.

That's why William Baxter and Vincent Scheib, two Carolina computer science graduate students working with computer science professors Ming Lin and Dinesh Manocha, developed dAb, a computer painting system that works and feels like the real thing.

In dAb, the artist's brush is a 3-D stylus, and her canvas is the computer screen. The stylus provides force feedback, meaning it feels like a real brush moving on canvas, Scheib says. The artist can choose one of several virtual brushes—rounds, flats, brights, and more—that the developers modeled to perform like real-life paint brushes. Brush shape alters as the artist increases or decreases pressure on the stylus. The "footprint" of each brush is modeled to be predictable and lifelike, so the artist can control complex brush strokes just as she could with real brushes.

dAb allows the artist to load up her brush with complex blends of paint and to apply them onto the canvas in predictable and realistic ways. When it's time to mix colors or clean a brush, the artist simply taps her keyboard's space bar, and out pops a virtual palette. Another tap brings back the canvas. The paint model is bidirectional—paint can move from the brush to the canvas and vice versa.

The researchers even factored in drying time. The artist can control the blending of new paint layers into previously painted layers by allowing the paint to partially dry. She can dry the whole canvas instantly or let dAb dry it slowly.

Best of all, dAb is so intuitive that an artist can grab the stylus and paint without training. "Artists using our brush really think of it as a real brush," Scheib says. "They move it like they would a real brush, and they really imagine that it's a real brush in the computer."

hat do artists think of dAb? "Bill and Vince have worked hard to make the program as close to actual painting as possible—and I think they've definitely succeeded," says Rebecca Holmberg, a Carolina chemistry grad student who loves to paint. "In some ways dAb even surpasses wet painting. The capability to dry the canvas at any time and having a button to undo minor mistakes—that's an artist's dream."

"Art is more than just the final product," Baxter says. "It's a process, too, and that process can be of benefit. Many people paint for the pleasure of painting—the feel of the materials, the way their imagination slowly takes form on the canvas, the way the paints and the brush work together. So these people have no interest in pushing a button to have a computer create a painting for them."

Lin says the team's ultimate goal is to enhance the level of usability for computer interfaces such as dAb. The team hopes that a virtual brush model like this one will be incorporated into future computer painting software for training and education, Manocha adds.

dAb is one of many research projects within the GAMMA research group headed by Lin and Manocha. Sponsors of GAMMA include U.S. Army Research Office, Department of Energy, Intel, National Science Foundation, and the Office of Naval Research.