Graphics Programs Reference
In-Depth Information
can capture detail in shadow values and highlight areas, as well as how well it
records the transitions between brightness levels within an image.
On a scale from 0.0 (absolute white) to 5.0 (absolute black) the range of a
device is dei ned numerically as the dif erence between the extreme values
of light and dark the scanner can manage. The higher the value, the greater
the scanner's ability to distinguish information in the shadow and highlight
regions. A dynamic range of 2.0 is of lower quality, while high quality drum
scanners can reach up to 4.6. Most l atbed color scanners have a dynamic
range between 2.4 and 3.2. The quality of a scanner's optics, in combination
with its bit depth, contribute to the dynamic range.
Scanning black and white i lm
Most scanners have a dii cult time scanning black and white negatives
because black and white i lm has a very small density range, typically less
than 2.0. Most scanners are designed to handle the 3.0 to 4.0 density range
of transparencies and therefore have to spread the range over 256 levels,
resulting in scans with poor separation in the shadows and poor gradation.
Tri-X 400 scanned with grayscale
For optimal results, and for the very same reasons it is best to capture in
color for digital BW conversions (see Chapter 4), it is also best to scan B&W
negatives using color positive settings. You will get far more information
out of the negative by using the four channels of capture with color settings
than you can using a scanner's B&W setting alone. Better results can also be
achieved by scanning the negative as a positive and inverting the negative in
Photoshop. A side by side comparison of two scans of the same image, one
scanned in RGB and the other grayscale, will show you that the individual
Tri-X scanned in RGB as a positive
exhibiting far more detail in the
wrinkles of the socks than the
previous scan in grayscale
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