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What to Look for Scanner
Bit Depth
As with any sophisticated piece of technology, there are a
few technical aspects of scanners you'll want to understand
before you go shopping. One term you're bound to bump into
is bit depth. For each pixel in an image, the scanner can
remember a certain number of bits which is known as bit
depth. The higher the bit depth, the better the scanner is
at distinguishing between really close shades of the same
colour. This results in higher image quality.
The minimum bit depth for decent image quality is 24. So for
each pixel, the scanner remembers 8 bits of information for
each of three colour levels (red, blue and green). Overall,
this means the scanner can theoretically represent around
16.8 million colours.
Inherent in the scanning process is a certain loss or
distortion of information which is caused by a number of
factors. This is commonly referred to as "noise." In
practice, noise cuts 24 bit depth down to around 18 which
decreases the number of colours represented. As a result,
scanned photos will lose some image quality in the
highlights and shadows. But the average user with a regular
printer should find 24 bits adequate for most documents and
web graphics.
The next couple of steps up in bit depth are 30, 32, 36, 42
and 48. If you plan on getting a scanner for slides,
negatives or transparencies you need at least 30 bits, and
36 bits would be preferable. Now you might be wondering what
happens if you get a scanner with 30 bits, but your monitor
or printer can only handle 24 bits of colour data. The extra
information at higher bit depth will still produce smoother
colour gradations and better overall image reproduction.
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