Normally the row of sensors on the Coolscan looks just once at each pixel of the image it is scanning. (That's not exactly true, but it'll do for the moment.)

The CCD sensor that looks at each pixel is an analogue device. Hardware then turns that reading into a digital number. Usually the reading is an accurate reflection of what the sensor saw. Statistically the number will sometimes be wrong. With normal colours that won't happen very often. But on the edges of the normal range for the sensor, there's a greater likelihood of random noise values.

When Multi Sample Scanning is used, the same spot is sampled a number of times. The more often it is sampled, the more likely that the scanner will return an accurate value rather than a noise value. (If it looks at a spot 16 times, three values might be noise, but 13 will be accurate. The software will average all the values. Which will be more accurate than a single reading.)

Coolscan LS-2000 Motor Problem

With my Nikon Coolscan LS-2000 after it was shipped to and from Nikon for repairs I found that my images has 'staircase' effects, so edges weren't sharp. Apparently the LS-2000 had a motor that could becone disjointed (not a technical term). Scanning pictures with multi-scanning set to 8 seemed to totally cure this problem. That's one of the reasons why I think my LS-2000 is very, very slow: I always have to scan images eight times. Even on a single scan it's much slower than my 5000ED. With Multi-Scanning set to 8 it takes 15 minutes to scan a single image.

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