Highest Quality Capture: Workflow Phase I - Black and White in Photoshop CS4 and Photoshop Lightroom - page 65

Flatbed Scanners
These scanning devices are much like Xerox copy machines in that you lay the
print or negative down on a sheet of glass and close the cover. The scanner
illuminates the print or negative from under the glass allowing the CCD to
capture the image line by line. Flatbed scanners can scan prints and i lm
(using optional transparency adaptors).

Print/Sheet Fed Scanners
These scanners were originally designed for snapshots, although some can
also scan slides and i lm. They are similar to l atbed scanners, however the
image is fed into a slot instead of laying l at. The CCD reads the image line by
line as the image is drawn past a stationary CCD. Sheet fed scanners take up
mush less space than l atbeds, however you will not be able to scan images
from topics or magazines.

Resolution: optical vs. interpolated
Resolution describes how well a scanner can capture image detail. For
the technically adept, a scanner's resolution is determined by how many
pixels per square inch the scanner can read in each direction. By dividing
the scanner's surface into square inches, a typical scanner might sample
300 pixels vertically and 300 pixels horizontally for a resolution of 300x300
ppi (pixels per inch) producing 90,000 readings per square inch. Higher
resolutions would produce higher readings per square inch, and therefore
capture greater detail. Many desktop scanners can produce scans up to 4600
pixels per inch optically.

Optical resolution is the true measure of a scanner's quality and therefore
produce the purest data. Interpolated resolution is the higher resolution a
scanner achieves by adding made up data and pixel information to the optical
resolution, by guessing with advanced algorithms using photo editing software.

Bit depth
While resolution measures how many pixels per inch a scanner captures, bit
depth refers to how much information the scanner records for each pixel, that
is, the number of bits used to represent each pixel. Greater bit depth allows
more shades of gray and colors (see “Bit Depth”, page 34 for more information).

Note:
Many scanners have
an optical resolution
(true resolution) and an
interpolated resolution
where image data is
resampled (or made up)
to create larger i les. Be
sure to research your
scanner specii cations
to i nd the optimal
resolution of your
scanner.

Most scanners on the market can scan up to 24-bit, but more and more are
appearing that have even greater bit depth. Though not many systems can
represent all the color possibilities such scanners provide, the greater bit
depth does allow the scanner to pick up more detail in dark areas of an image,
and it can help reduce noise in the i nal image.

Dynamic range
Dynamic range refers to the tonal range of the scanner from light to dark
extremes. A scanner's dynamic range measures how ef ectively the scanner