DOTMATIC CALIBRATION

Greg Imhoff used a simple rubber ball to illustrate a complicated, even controversial concept involving a classic calibration procedure. By asking an assistant to bounce the ball on the floor, he sought to show attendees the microscopic flaw hidden within newspapers’ densitometer use.

First, the ball was bounced straight up and down. That, Imhoff argued, represents how light waves reflect back from film -- a virtually flat surface. A ball bounced at a slight sideways angle, by contrast, mirrors the distortion caused by the grain profiles inherent in plate surfaces.

“Plates have grain profiles, films do not,” said Imhoff, president of Grip Digital Inc. of Western Springs, Ill. “They have 3-D surfaces, just like the moon or the Rocky Mountains.”

A similar assessment comes from a more authoratative source than a toy ball, according to Imhoff. Plate manufacturers use planimeters, not densitometers, to test their products -- a system too labor-intensive and costly to put into practice in production, he argued during a Thursday afternoon Press & Materials session.

Enter the Dotmeter, a handheld contraption vaguely resembling a cell phone but actually including a charged-couple device and a 7,000 dot-per-inch scanner. Unlike densitometers, which measure the light reflected back from a dot and convert the result into an analog signal, the Dotmeter shoots, scans and electronically calculates the actual dot area. Like a planimeter, it can also identify which areas on the plate are ink-accepting.

By contrast, visual guesswork yeilds a 10 percent margin of error, a loupe 5 percent and a densitometer about 3 percent -- still enough to wreak havoc in four-color printing, Imhoff argued.

The technology works equally well with analog and computer-to-plate systems, though it may prove far more useful with the latter technology since CTP eliminates the film step. And the Dotmeter’s digital results have broader implications, according to Imhoff, who envisions the TIFF images it generates someday being used to linearize CTP operations at the RIP and perform quality control over the Internet.

-Mark Toner