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The Ins . . . Move Your Workflow Forward with Large-Format Scanners (Cadalyst Labs Review)
1 Apr, 2007 By: Henrik VestermarkCadalyst Labs examines the latest large-format scanners from Colortrac, Contex, Graphtec, GTCO CalComp, Oce and Paradigm Imaging.
It's been one year since Cadalyst last looked at large-format scanners and more than two years since it published a large-scale comparative review. New scanners have arrived on the market, and it's about time we review these latest products with regard to CAD users' needs. But what are those needs?
Most large-format scanners are color scanners, yet less than 10% of CAD users have a well-defined need for color scanning. If anything, most buyers are looking at color scanning only to hedge against future needs, but they're not willing to pay a premium price for features that they might need some day. And even though today's CAD scanning typically requires a 200–400dpi range, most scanner manufacturers deliver units that offer resolution as high as 4,800–9,600dpi. Most CAD customers also need only 500–2,000 scans per year, something that can be done easily with less elaborate products. And when I scan an E-size drawing, does it really matter that it completes in 6 seconds as opposed to 18?
Scanning speed may not be an issue, but total cost of ownership is. On average, a new scanner should last five years (which also is the depreciation period for most companies), so it becomes important to figure out the actual purchase price plus the total cost of operation during those five years. Most CAD buyers are looking for a scanner purchase that maximizes value.
Cadalyst invited the traditional scanner manufacturers to participate in this review. Colortrac, Contex, Graphtec, GTCO CalComp, Océ and Paradigm sent scanner models suitable for the CAD market. All offer warranty options for five-year periods. All of Contex's on-site warranty options are handled by local distributors or dealers.
In general, the state of the scanner market is good for today's CAD community. All of the tested scanners passed the minimum requirements for the CAD industry—but I found no slam-dunk winner. All scanners have advantages and disadvantages, and individual users must evaluate each based on their personal preferences.
Testing Procedures
First of all, abandon the myth that optical resolution is equal to scanning quality. Optical resolutions are indicators of scan quality, not measures of it. To measure the quality, you must also consider a scanner's optical system, mirrors, CCDs (charge-coupled devices), glass plate and the illumination systems. For this review, I measured scanning quality by seeing how many line pairs per milli-meter each scanner could resolve in scanning resolutions between 200 and 400dpi. This value gives a better idea about a scanner's performance potential, rather than just relying on the optical resolution.
Next, I looked at each scanner's vertical and horizontal accuracy. I didn't measure a full 36"—rather, I measured a randomly selected 6" distance within the scan area. Most scanner vendors electronically adjust the 36" distance to match within ±0.1%, but only one of the vendors tried to calibrate each individual pixel. As expected, I obtained below-scanner specification accuracy, but I found it to be a much more realistic value for a scanner working in a CAD environment.
Finally, I looked at scanner performance and measured scanning speed. To do this, I started the clock each time I pressed the scan button and stopped it when each image had been scanned, converted to the destination file format and saved to disk. I saved black-and-white scans as the industry standard TIFF Group 4 file format and grayscale images as TIFF uncompressed. I then measured scan speed for scanning resolutions of 100, 200, 300, 400, 500 and 600dpi and took the combined average scan time for the 200-, 300- and 400dpi speeds because these resolutions are the most commonly used in the CAD industry. The measured scan speed is far from the scanner manufacturers' specification because I measured real-world times that take into consideration the USB scanner interface, PC compression, saving of the file format and the notorious lag time that exists between pressing the scan button and having the scanner actually scan the first line of data. This pause is typically 2 to 3 seconds. All scanners seem to have this lag time.
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About the Author: Henrik Vestermark
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