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Scanners typically read red-green-blue
color (RGB) data from the array. This data is then processed with some
proprietary algorithm to correct for different exposure conditions, and sent to
the computer via the devices input/output interface (usually SCSI or bidirectional parallel
port in machines pre-dating the USB standard). Color depth
varies depending on the scanning array characteristics, but is usually at least
24 bits. High quality models have 48 bits or more color depth. The other
qualifying parameter for a scanner is its resolution,
measured in pixels per inch (ppi), sometimes more accurately
referred to as Samples per inch (spi). Instead of using the
scanners true optical resolution, the only meaningful parameter,
manufacturers like to refer to the interpolated resolution, which is
much higher thanks to software interpolation.
As of 2009,
a high-end flatbed scanner can scan up to 5400 ppi and a good drum scanner has
an optical resolution of 12,000 ppi.
Manufacturers often claim interpolated resolutions as high as 19,200 ppi;
but such numbers carry little meaningful value, because the number of possible interpolated
pixels is unlimited.
The size of the file created increases with the square of the resolution;
doubling the resolution quadruples the file size. A resolution must be chosen
that is within the capabilities of the equipment, preserves sufficient detail,
and does not produce a file of excessive size. The file size can be reduced for
a given resolution by using "lossy" compression methods such as JPEG, at some cost in
quality. If the best possible quality is required lossless compression should
be used; reduced-quality files of smaller size can be produced from such an image
when required (e.g., image designed to be printed on a full page, and a much
smaller file to be displayed as part of a fast-loading web page).
The third important parameter for a scanner is its density range. A
high density range means that the scanner is able to reproduce shadow details
and brightness details in one scan.
By combining full-color imagery with 3D models, modern hand-held scanners
are able to completely reproduce objects electronically. The addition of 3D
color printers enables accurate miniaturization of these objects, with
applications across many industries and professions.