Nikon D300 Complete Manual page 415

In the top row of resolution patches just to the left of the
seven you can see some irregularity as the frequency of the
detail starts to exceed the capture ability. You can see it even
more clearly in the second row of diagonal line resolution
samples below the 5, 6, and 7.
The usual technique for sharpening images is to apply a
technique called "unsharp masking," and a variation of that
technique is used by the D300. Unsharp masking finds edges
by looking for adjacent pixels with value differences. On the
brighter side of the edge, unsharp masking lightens the pixels;
on the darker side, it darkens the pixels.
Most unsharp mask filters have settings for amount (controls
how much lighter or darker the values are made), radius
(controls how wide an area over which the value shifts are
made), and threshold (controls how much of a difference
there must be between adjacent pixels before adjustments are
made). The D300 doesn't let you set the individual
parameters of the sharpening control; instead, you set an
overall "level."
The D300 has eleven possible sharpening levels (set via the
Picture Control setting; see "Picture Controls" on page
<334>):
A—(Automatic) The camera determines the appropriate
amount of sharpening to apply.
0—The camera applies no sharpening to the image data.
1 through 9—The camera applies a level of sharpening
you specify, ranging from a low amount (1) to a high
amount (9).
Thom Hogan's Complete Guide to the Nikon D300
Unsharp masks work by exaggerating edges. I
started with a medium gray block on the left
and a dark gray block on the right, and then
applied an Unsharp Mask. Note how on the
lighter side of the image the edge was made
even lighter, while on the dark side of the edge
it was made almost black.
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