Section III Digital Postprocessing
424
of merely copying the information, however, it
blends it with the color and texture of the area
surrounding the defect. Since the blending makes
the repair virtually invisible, this tool works very
well for removing small skin defects in portraits
and similar situations.
As noted in Chapter 14, Image Input and
Scanning, many scanners offer a feature that
automatically cleans up dust spots and scratches
during the scanning process. This can be a real
timesaver, especially if the original is in poor
condition from improper storage.
Most image editing programs offer a tool
that can be used to automatically clean up scans
from images that exhibit a large number of such
defects. In Photoshop, the tool is called the
Dust &
Scratches
filter, Figure 15-44. This filter actually
works by blurring pixels in small bright areas
(which are usually dust spots or scratches), but
can cause an undesirable softening of the entire
image.
Two settings in the dialog box for the
Dust
& Scratches
filter allow you to select the degree
of change. The radius setting determines the
width of the defect that the program will identify
as a spot or scratch. The larger the number, the
more blurred the image will be. The threshold
setting sets the sensitivity of the filter—how
much the color of the spot must differ from its
surroundings to be considered a defect. If the
setting is 1, the filter would consider everything
a defect and blur the whole image; a value of
255 would have the opposite effect—no defects
would be recognized and nothing would be
changed. Checking the
Preview
box allows you to
see the amount of blurring and spot elimination
done at various settings. Because of its effect on
image quality, this filter should be used only for
images that show a very large number of defects.
Although it can be tedious, cleaning up spots and
scratches with the
Clone Stamp
tool will preserve
the quality of the image.
Sharpening the Image
One technique available in the digital
darkroom that has no conventional darkroom
counterpart is sharpening, which involves
enhancing edge contrast to make the image
appear more sharply focused. While it cannot
correct an image that is badly out of focus, it
Figure 15-44. The
Dust & Scratches
filter can clean up
images with many small defects, but also can soften
the image unacceptably. A—This image of a newspaper
reporter was scanned from a Polaroid print made in
the 1960s. Note the many small white spots on the file
cabinet at left and on the screen of the television set.
B—Applying the
Dust & Scratches
filter at the settings
shown minimized the white spots, but seriously
softened the image. Before using this filter, you should
experiment with different radius and threshold settings
to see their effect.
A
B