Other aspects include the speed which the data transfers from the scanner to the computer and the degree to which the scanner distorts the objects it digitizes. The less the distortion, the higher the price tag typically.... So how does one 'benchmark' this intangible distortion? Well we came up with the following tests to help determine which scanner delivers the best image performance, after all dpi specs can be specified, the distortion is a bit harder to quantify, and not something that is immediately noticeable.

First of all, before we go any further, we measured the glass surface, and compared it to the actual scanable area. Some scanners have large glass surfaces with sections that are totally unusable. The HP ScanJet we tested faired excellently (as we expected it would considering its high cost). The glass measured 225mm x 365mm, and the actual scanable area was 217mm x 355mm. Except for a 10mm swath at the very front, and an 8mm slice on the left side, the usable area is almost entirely represented by the glass plate. Great!

Secondly, we measured the dimensional distortion caused by the optics in the scanner. As objects are moved from the center line of the scanner, the degree that light must be reflected to hit the sensor increases and with it comes dimensional distortion. We decided to test this distortion by scanning in a strip of graph paper (210mm x 44mm) once parallel to the center line (and centered on it), then perpendicular to the center line and lastly at a 45 degree angle. All images were scanned in at 100% enlargement and then rotated in a graphic program so they were all parallel to one another for easy comparison.

Ideally, all three images should be exactly identical. If they differed, then they would serve as a quantitative demonstration of the scanners' limitations.

In the case of the ScanJet 6100C all three strips were virtually identical. The parallel and perpendicular test strips are the exact same length, and the angled test strip shows true 90 degree boxes, and not rhombus's upon rotation.

Thirdly, we tested the ability of the scanner to enlarge a document. Going in appropriate steps of percentage, we hoped this would demonstrate the subsequent drops in image quality as the document was enlarged by the scanner. The higher the image quality of the enlarged section, the better the scanner proved itself to be.