Digital Prints

(Most modern scanners are 12-bit scanners. Even some that say they’re 16-bit are really
only using 12 bits of data carried in a 16-bit format that is more efficient for computers.)
Aren’t these millions and billions of colors simply overkill? Maybe, if you consider that
until recently with the introduction of Adobe Photoshop CS, almost no one could edit or
work with these high-bit files, and consequently, they were always down-sampled or converted
by the scanner into 24-bit images. However, the advantages of adding more information
up-front (more raw material or “headroom” to work with) in the scanning stage
has become more obvious to people, especially those working with film versus those scanning
prints where the density range is much lower (see below for more about that).
Keep in mind that many high-bit scanners still output the files in 24-bit (some do true
48-bit output). Why only 24-bit output? Because humans can’t really see 48 bits, and also
because computer monitors operate in 24-bit mode (although most digital printers can
accept 48-bit data, which is usually converted on the fly to 24-bit).
However, you still want to be scanning in high-bit mode because a 36-bit scanner has more
steps in the range of densities between deep shadows and light highlights than does a 24bit
scanner. (Truthfully, there are no more 24-bit scanners; they’re either 36-, 42-, or 48bit.)
A 24-bit scan means 8 bits per RGB channel, which equates to 256 possible brightness
levels per channel (0–255, where 0 is pure black and 255 is pure white). A 36-bit color
scan means 12 bits per channel or 4,096 possible values. That’s a lot more tonal possibilities.
And this is especially important in the dark shadows of positive or reversal film (which
with negatives turn into highlights) where you want as many steps to differentiate unique
detail as possible. Shadow detail is frequently what makes or breaks an image.
The downside—and there’s always a downside—to scanning and then editing high-bit image
files is that increasing the bit depth increases the file size arithmetically. However, as scanning
expert David Coons says, “Double the file size is a small price to pay for the 256-times increase
in luminance accuracy you achieve by moving to 16-bits per channel.”
Dynamic Range
Many people get the terms color or
bit depth and dynamic range confused.
Both are important and
related, but they are different. Think
of a stairway: the number of steps is
a function of the bit depth (8-bit
equals 256 steps), and the height of
the entire stairway is the dynamic or
density range from Dmin to Dmax
(see Figure 3.2).
Scanning book author Wayne Fulton
(see more about him later) has an
even better analogy when he says,
“More bits are needed simply to store
data with high dynamic range, but
the bits do not create dynamic range,
Chapter 3 ■ Creating and Processing the Image 77
Figure 3.2 The digital stairway. The
number of steps is a function of Bit
Depth; the height of the stairway is
the Dynamic/Density Range.