V1.02
Thom Hogan’s Complete Guide to the Nikon D300
Page 144
rendered image and do additional post processing on it.
Left: a histogram from an image using Photoshop’s Levels
command. Right: the same image overly manipulated, which
reveals big posterization (gaps) in the darker levels. Posterization of
highlight detail makes for detailless highlights; posterization of
shadow areas makes for blotchy looking shadows. Once image
data has been posterized, each additional manipulation can
compound the problem.
For example, one typical problem found by D1x users was
that they’d underexpose slightly to make sure highlights were
properly captured, and later use a Curve to reshape the tonal
ramp (similar to what the example shows above, actually).
Unfortunately, posterization in the shadow detail would often
then become visible, resulting in a blotchy, muddy look in the
darker areas of the image. By keeping the in-camera
manipulations in 16-bit data, the D300 avoids this problem.
Shadow detail in JPEGs made on a D300 is much better than
most previous Nikon DSLRs (though it can be a bit noisy at
higher ISO values if noise reduction isn’t turned on).
JPEG Artifacts
JPEG compression produces two primary types of visible
artifacts. The higher the compression used, the more visible
these artifacts tend to be. Also sharpening set to high levels
tends to trigger these artifacts.
The first artifact is best described as “visible blocks” (see
example, below). Visible blocks are created because JPEG
operates on images in 8x8 pixel blocks.
Blocks are most often seen in areas where there is little detail
but a continuously variable color (shading on an unevenly lit
wall, for example). The quantization step attempts to throw
