Section III Digital Postprocessing
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The three sliders control the effect of the
filter. The amount can be adjusted from 1 to 500
percent, but most often, it will be set somewhere
in the lower middle part of that range, from about
100 to 200 percent. Higher values are typically
used with larger images that will be reproduced
on inkjet or dye sublimation printers; lower
values on smaller images, especially if they will
be reproduced by the halftone printing process
(for example, in a magazine).
Radius settings can be varied from 0.1 pixels
to 250 pixels. At the lower values, sharpening
is confined mainly to edges within the image;
settings of 5 pixels or lower are normally used.
The
Threshold
setting identifies how much
different in brightness level two pixels must
be before sharpening will be applied. The
adjustment range is 1 to 255, with the number of
pixels affected decreasing as the setting increases.
A typical starting point for
Threshold
settings is
3 to 4.
Sharpening should be done as the final
step before printing, after all other adjustments
have been made to the file. If sharpening is
applied earlier in the process, additional image
changes could exaggerate its effects. For example,
increasing file dimensions after sharpening
could make the edges of objects appear to be
oversharpened.
Sharpening layered images
If an image has more than one layer, the
layers must be sharpened individually (or
the image flattened to a single layer before
sharpening). Only “content” layers can be
sharpened, however. If the image includes an
adjustment layer, there would be no visible
effect when that layer is selected and sharpening
is applied. Sharpening has no effect since an
adjustment layer has no pixel content to be
sharpened.
Figure 15-47 shows a file with a total of three
layers. Sharpening this image is a three-step
process: each layer is selected and sharpened
individually. An advantage of this method is the
ability to independently sharpen layers (or even
selected portions of layers). Depending on the
image content and your artistic intent, different
amounts of sharpening could be applied.
Figure 15-46. The effect of different unsharp masking
percentages can be viewed directly on the monitor.
Unsharp masking is the most effective sharpening
method.
Figure 15-47. Sharpening an image with several layers
must be done on a layer-by-layer basis. As indicated by
the highlight in the
Layers
palette, the sharpening is
being applied to
Layer
2, the active layer.