…Standing on four metal legs, under two banks of fluorescent lights, was what appeared to be a modest-size billboard, measuring about 9 feet wide by 4 feet in height. Across its face, which looks like paper under glass, was a full-color advertisement for a soft drink maker. A few moments later the ad disappeared and was digitally replaced with a different one, and then another, like a screensaver cycling through images on a laptop computer screen.

But the surface of this billboard is not a liquid crystal diode screen - the energy-hungry display common to laptops and increasingly to cellphones, digital cameras, digital organizers and flat-screen computer monitors and television sets. Neither does this billboard share the light-emitting-diode technology that makes million-dollar-plus video screens light up the night in Times Square, Las Vegas and sports arenas around the world.

What makes the electronic billboard in Jersey City possible (and those installed for trials in London, Tokyo, Toronto and Panama City, among other locations) is an innovation by a New York-based display technology company whose name, Magink, is a combination of the words magic and ink. Its approach to imaging departs from the way most text, graphics and images are electronically presented, including the way expensive plasma screens work, as well as cathode-ray tubes, the old workhorses still found in most television sets and desktop computer monitors.

By creating a paste made of tiny helix-shaped particles that can be minutely manipulated with electric charges to reflect light in highly specific ways, Magink can produce surfaces that look like paper but behave like electronic screens, rendering high-resolution, full-color images without ink - or, as Magink executives like to refer to the process, with digital ink.

Magink prototype screens are capable of displaying video images at more than 70 frames a second, twice the speed needed to produce smooth, cinematic motion. But the digital images share so many of the characteristics of paper, its makers say, that they are easily viewed in bright sunlight but must be lighted much like conventional billboards when there is little light.

…With the new digital technology, Mr. McConnell said, a client could change its billboards several times a day - say, a fast-food chain, to promote its breakfast, lunch and dinner meals. And the process - from idea to installation - could be shortened from weeks to overnight, he said.

While Magink billboards cost far less than large-scale video screens, they are not inexpensive, Mr. McConnell said. One sign he is testing, measuring about 10 feet by 20 feet, cost $80,000. A standard billboard of about equal size would cost about $10,000, but would also require costly installation crews to change displays. More significantly, advertising companies could sell space on the billboards by the hour.

Mr. McConnell said that when the signs are mass-produced, their prices are likely to drop.

And then there are the power savings, proponents of digital ink displays are fond of pointing out. While the screens offer some of the flexibility of large video screens, they do not emit light and therefore require little energy to receive and make changes in their images and text.