Testbed and Methods

According to your feedback, my method of testing scanners is acceptable for you, although some readers ask why I don’t use resolution targets to determine the “real resolution” of the tested devices”. Well, I don’t have such targets and moreover I don’t think it is appropriate to use them. This way of testing is subjective since such evaluations are performed “by the eye”. It is more correct to examine the modulation transfer function (MTF) and measure the scanner’s optical resolution through it. This would also reveal how well the scanner’s optical system reproduces required frequencies. I’m going to add a section with such a test soon. As yet, my testing consists of the following steps:

• Determining the real scanning speed when digitizing standard originals;
• Calculating noise coefficients in the digitized images to estimate the scanner’s electronics’ tolerance to interference;
• Finding gamut ranges of the scanners with transparent and opaque originals;
• Constructing graphs of the color difference between a color target and its scan.

The configuration of the testbed remains the same from test to test, so you can compare the results with those I got in my earlier reviews. The testbed:

• Intel Pentium 4 3.00GHz CPU;
• 1GB DDR SDRAM;
• Intel Bonanza D875PBZ mainboard;
• ATI RADEON 7000 graphics card;
• IBM Deskstar DTLA-307015 HDD;
• Samsung SyncMaster 757 NF monitor;
• Microsoft Windows XP Professional SP1.

Scanning Speed

I mentioned above that both tested models share almost identical mechanics, but have quite different mechanical resolutions and thus should differ in the scan speed. To put it roughly, the employed sub-scan technology Micro Step Drive moves the carriage of the Perfection 3170 in 6400 steps, and the carriage of the Perfection 4180 in 9600 steps. So, theoretically, the second model should be slower than the first. I checked this out in practice, performing various scan jobs and measuring the time with an ordinary stop-watch. I used the following scan resolutions: 300dpi, 600dpi, 1200dpi and 2400dpi. Here are the results:

You see my words are confirmed: the Perfection 4180 does take more time to perform a job than the Perfection 3170. Here are more numbers I didn’t include into the diagram above:

• The Perfection 3170 model takes 1 minute 14 seconds to digitize a 35mm slide at the optical resolution (3200dpi); the Perfection 4180 produces the same scan at the same resolution in 1 minute only;
• The Perfection 4180 takes 1 minute 46 seconds to digitize a 35mm slide at its optical resolution (4800dpi);
• The Perfection 4180 takes 25 minutes 20 seconds to digitize a 4x6” photograph at its optical resolution (4800dpi).