|
|
What to Look for Scanner
Dynamic Range or Optical Density
For those of you who need a good graphics scanner or want
really high image quality, you need to consider dynamic
range, also called optical density (OD). It is a measure of
how well the scanner can capture the tonal range of an
image, the gradations from bright highlights all the way to
dark shadows. Dynamic range is measured on a logarithmic
scale (like the Richter scale) from 0-4 with zero as pure
white and four as pure black. Dynamic range is the
difference between the darkest and brightest optical
densities a scanner can capture. The bigger the difference
the larger the dynamic range.
Most flatbed scanners have an OD around 2.8-3.0 which is
fine for the tonal range of photographs. To scan slides,
negatives and transparencies which have broader tonal ranges
you need a higher OD. For slides and transparencies aim for
3.2, a bit higher at 3.4 for negatives. When comparing
scanners with the same bit depth, choosing one with a higher
dynamic range will give you better image reproduction.
However, many scanners aimed at the average user do not
report dynamic range so don't be surprised if you can't find
it in the specs.
|
|