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Section III Digital Postprocessing
Figure 15-36. Converting from color to grayscale. A—The original color image. B—A straight conversion using the
grayscale command can result in a flat image because of similar brightness values of different colors. C—Selecting
the best color channel and converting it to grayscale can provide better contrast.
A B C
Figure 15-35. You can use the
Color Replacement
tool
brush to paint a new color over an object while retaining
the original surface texture. The crosshair in the center
of the brush circle is placed on the color to be replaced.
A mouse click will then make the color replacement in
the area covered by the brush circle.
color to a shade of gray, similar brightness values
make it difficult to distinguish a red flower from
its background of green leaves. Further processing
of the converted image using
Levels
or
Curves
can
improve the contrast.
An alternate conversion method that often
gives better contrast is to review the color
channels (which are displayed in grayscale)
and select the one that looks best. With the
desired layer selected, the
Grayscale
command
will use the brightness values of that channel
to make the conversion. Figure 15-36 shows the
results of the two conversion methods.
When the
Desaturate
command is
used, Figure 15-37, color is removed from
the image, and gray values are displayed.
The image remains in the color mode, with
the three color channels still intact. This
situation increases the possibilities for image
manipulation, such as adding areas of color
or restoring some portions of the image to
their original color values (see Using the
History Brush, in Chapter 16).
To desaturate only part of an image so that
some areas are gray and others in color, two
different techniques may be used. A selection
may be made to isolate the desired part of the
image, and the
Desaturate
command applied
to the selected area. Direct desaturation can be
done with the
Sponge
tool. This tool, located
with the
Dodge
and
Burn
tools on the toolbox,
is applied like a paintbrush or eraser tool to
the desired area. Opacity can be set to 100