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Closing the Gap
Flatbed scanners give drum a run for it's money


Author:  Hans P. Hogers
Reprinted from the January 1998 issue of Canadian Printer magazine

Flatbed scanners keep learning new tricks. And with each trick they learn, the gap between high-end flatbeds and the top-of-the-line drum scanners gets a little bit narrower. Lately that gap has been getting very narrow indeed. The two machines that come closest to eliminating the gap are probably the Fuji Lanovia and the Screen Cezanne, both of which use xy and zoom technology and achieve a dynamic range of 0 to 3.9. But before we look at these machines, and at other flatbed and drum models, it might be useful to examine the limitations of flatbed scanners and the ways that manufacturers are overcoming these limits.

At the heart of every flatbed scanner is a CCD (charge-coupled device) sensor, the flatbed's equivalent to the photo-multiplier tube (PMT) used by drum scanners. Currently the CCDs in flatbeds incorporate 6,000 to 8,000 elements, but new CCD chips are now available from Kodak, Sony, NEC, and Toshiba containing more than 10,000 elements.

The number of elements determines the highest dot-per-inch resolution the scanner is capable of. A traditional A3 flatbed scanner with a 6,000 element chip and an 11-inch-wide bed can offer a maximum dpi of 6,000/11, or about 545 dpi. That's because the CCD chip has to scan the entire width of the bed with every pass. Upgrade to an 8,000 element chip and maximum dpi becomes 8,000/11, or about 725 dpi.

A further limitation to the resolution of such scanners is caused by lens distortion at the edges of the scan. Only a central strip running up the scanning bed experiences the full resolution.

One way to increase the resolution would be to narrow the width of the scanner bed so that the CCD elements have less territory to cover. With a 4-inch-wide scanner bed, resolution would be 8,000/4, or 2,000 dpi. That's a respectable resolution, but an impractical narrow bed for a multi-purpose scanner.

XY and Zoom Technology

Current high-end flatbeds use two technologies­xy and zoom­ to effectively narrow the width of bed the CCD has to deal with. And they do this without limiting the actual physical width of the scanning area.

Scanners with xy technology can move the scanning head in two directions­forward and backward (x), and left and right (y). That lets them make multiple passes up the scanning bed, each time scanning a narrow strip of the bed at a high resolution. If the original being scanned is wider than that strip, software stitching is used to line up and consolidate the strips. Scanners using this technique include the Purup-Eskofot EskoScan 1318, and the Scitex EverSmart line.

The EskoScan 1318 offers a resolution of up to 5,080 dpi over a scan area of 11 x 17.3 inches. It can be used for colour scanning, and the dot for dot scanning of pre-screened materials. Dot for dot scanning has been a specialty of Eskofot scanners, but is now being offered by an increasing number of other manufacturers.

Scitex says it sold 1,000 of its EverSmart scanners in the first six months since product release in Spring '97. EverSmart Pro units can scan up to 70 35mm images in one batch with an optical resolution of up to 3,175 dpi over the entire format. The scanners are driven by a Power Macintosh with PCI bus, and can process 20 CMYK 6 x 7 cm scans an hour at 250 percent and 300 dpi.


"We tell the customers looking at drum scanners that we have the same scanner, same speed, but on a flatbed. Of course some will still pick the drum. It's like car transmissions; some people still prefer a stick."

--Mamoud

Zoom Lenses

Another way that scanners are effectively narrowing the width of the scanner bed for increased resolution is through the use of zoom lenses. By focussing in only on the image being scanned, the scanner can devote the entire width of the CCD chip to one image instead of wasting CCD elements on parts of the bed that contain no image. One of the limitations with zoom technology is that maximum resolution is still only available in a band at the centre of the bed. Also, in batch scanning situations, the resolution is determined by the width of the entire batch of scans and not by the individual images. This technology is used by the AgfaScan T8000, and the Heidelberg Topaz, which has been one of the most successful A3 size high-end CCD scanners.

The AgfaScan T8000 features an optical resolution of from 666 to 8,000 dpi and uses a mirror-less five-lens design. A built-in cooling system reduces thermal noise in the CCD.

Heidelberg says it has sold 4,000 of its Topaz scanners in the last two-and-a-half years. Introduced at Graph Expo East in 1994, the units offer an optical resolution of up to 5080 dpi, and can be configured for dot to dot scanning.

Most recently, xy and zoom technologies have been combined in the Fuji Lanovia and the Screen Cezanne. This combination allows the scanners to provide very high resolution (zoom technology) over the entire width of the bed (xy technology).

The Fuji C-550 Lanovia had not yet been released at press time, but the company says it will provide up to 5,000 dpi resolution regardless of the original's position on the bed. The scan head moves to the best position for each scan, then the zoom lens focuses the original over the width of the CCD. Dot for dot scanning is not yet available, but is planned for later this year.

Screen's Cezanne scanner was introduced in Fall '97. According to Javier Mahmoud, dealer relations manager with Screen (USA), Chicago, the company sold 150 of the units at Print 97.

Screen also manufactures drum scanners, but Mamoud says that the Cezanne will make them harder to sell.

"The dynamic range on the Cezanne is from 0 to 3.9, and the dynamic range on our drum scanners is 0 to 3.9," Mamoud says. "We tell the customers looking at our 1045 A1 drum scanner that we have the same scanner, with the same speed, but on a flatbed. Of course some of them will still pick the drum. It's like car transmissions; some people still prefer a stick."

One of the features that makes the Cezanne an 'automatic' rather than a 'stick' is the artificial intelligence software, which learns from the corrections that the operators make. The auto-learning function can be turned off for corrections to unusual originals.

But what if you do prefer a 'stick?' Can drum scanners take you further than flatbeds?

Flatbed scanners are "90 percent of the way there," concedes Edward Chrusciel, president, Optronics International Corp., Chicago. But he says there has been a resurgence of interest in drum scanners as users realize the limitations of CCD technology.

Image archives of stock photography are a healthy market for drum scanners, Chrusciel says, because these scanners provide the most dynamic range and colour fidelity.

Drum scanners are also less likely to pick up dust and other artifacts since they focus tightly on the surface of the original. Flatbed scanners have a greater depth of field, so they can see past the surface to the dust and scratches.

Recent drum scanners include the Heidelberg Tango, which uses LinoColour software running on a Macintosh to provide what it calls "one button" scanning. The Tango incorporates an upright, or vertical, drum, something first offered by ICG. The recently introduced ICG 360 scanner uses a drum spinning at 1,800 rpm and provides an optical resolution of 12,000 dpi.

Presumably the falling scanner prices that designers are experiencing will have an effect on the prices that prepress users see.

Cost Savings

Flatbed scanners can't match those specs, but for many printers and prepress operations it's hard to argue with the flatbed's cost effectiveness.

"I think CCD scanners have already taken over from drum scanners for a high percentage of the market," says Nicky Milner, technology director, Quebecor Printing, Toronto. "Drum scanners can still be visibly different in extremely large blowups, where effectively what you're doing is scanning at 8,000 dpi, and they can still extract a slightly better dynamic range, so you can play more games if you have a lot of shadow detail. But if have an excellent original that you're not blowing up much more than 400 percent, you can't make out a lot of difference between a CCD and a drum."

Flatbed scanner prices have been plummeting at the low end. Recently, some flatbed scanner/Photoshop bundles have been selling for less than the price of Photoshop itself. Presumably the falling scanner prices that designers are experiencing will have an effect on the prices that prepress users see.

Umax has already introduced a $US7,000 scanner targeted at printers. The Powerlook 3000 uses a dual-lens system that provides a single zoom step for an optical resolution of 3,048 dpi.

Unfortunately, it may take some time for the ripples to reach the high end. The market is small, and the components are expensive.

"At the higher end you have to apply the same craftsmanship to a CCD scanner that you do to a PMT device," notes Evan Cambray, marketing manager Fuji Graphics Systems Canada, Toronto. "They contain costly features like quality optics, close manufacturing tolerances, and frames that are cast, not riveted. This is going to dictate that these devices will remain expensive."

Which at least will keep high end scanners out of the hands of designers. For now.

"For the foreseeable future I think the professional scanner will still be doing the bulk of the scanning," says Frank Romano, a professor with the Rochester Institute of Technology. "But I think you can predict a moment in time, maybe in five years, maybe in 10 years, when users will do their own scanning. For that to happen though, we need excellent colour management. We're predicting that eventually people will scan RGB and use RGB everywhere in their system until it finally gets printed out. RGB would have more colour gamut, and would be compressed. CMYK files are gigantic."

Romano suggests that an RGB workflow won't happen until prepress operators and printers are able to trust that colour management will work and they'll get the results they expect.

"Lack of trust in colour management is why we still make CMYK so early in the process," Romano says. "We have to make sure that the colours are going to print properly."

Operator skill requirements are another barrier that will keep scanning in the hands of professionals for the near term, says Marg Macleod, president of IBEC Training, Toronto.

"Designers who want to make their own high-res scans are in for a shocking learning curve," she says. "Pleasing colour is not acceptable in many markets, and to do better than that you need a knowledge of colour theory, colour management, and the ability to anticipate what will happen as a scan goes through to outputting."

Whether it's drum or CCD, xy or zoom, a scanner is still only as good as the people who operate it.


We'd like to thank Canadian Printer magazine for giving us permission to post this article from their January 1998 issue. Visit their website to read more of their articles, join their mailing list or participate in their discussion group.
 

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