CHAPTER 12 THE IMPORTANCE OF RESOLUTION 185FIGURE 12.4
16-bit scans
must be con-
verted.
A low-bit scan, which has less information than a 48-bit scan, is compressed further
by any changes in Levels or Curves. The result is gaps that appear as brush bristles
in the image’s resulting histogram (see Figure 12.5). The edited image has dramatic
jumps in brightness levels, which result in posterization.FIGURE 12.5
Two histograms
of the same
image: a 24-bit
histogram after
tonal correction
versus a 48-bit
histogram after
correction.
Drawbacks to 48-Bit Images
A negative that is only 24×36 millimeters scanned at 2400 samples per inch at a
48-bit depth approaches 36 megabytes (MB) in file size. A medium-format negative
(6×7cm) can be upwards of 300MB! Modern G5 Macs and Pentium 4 PCs won’t have
too much trouble opening these large files, but edits can bog down even a high-end
system. Not only that, but some functions just plain aren’t available.