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Section III Digital Postprocessing
Changing canvas size
Sometimes, you need to increase the size of
the space around your image (think of the canvas
as the “base” on which your image rests). The
larger space might be needed to add a border,
or to increase the image content (by cloning or
copying) in one or more dimensions. This is done
by opening the
Canvas Size
dialog, Figure 15-13.
The uppermost section shows the current size
of the image, while the center section has
Width
and
Height
boxes, a
Relative
checkbox, and a grid
labeled Anchor. At the bottom, the color of the
canvas extension can be chosen.
There are two ways to specify the amount of
extension:
• With the
Relative
box checked, the amount
of increase (in inches or other units) can
be specified for both height and width,
Figure 15-14.
• With the
Relative
box unchecked, the desired
final width and height dimensions must be
entered.
If the
Anchor
grid is left in its default state
(with the gray square in the center), the canvas
will be extended as specified on all four sides
of the image. Moving the gray square to one
of the outside spaces will distribute the canvas
extension in other ways. See Figure 15-15.
The color of the extended canvas is selected
at the bottom of the dialog. The default is the
Background
color in the
Toolbox
(which is
normally set to white). A drop-down menu
allows you to select the
Foreground
color, white,
black, gray, or a custom color.
Working with Layers
One of the most attractive features of the
more sophisticated image editing programs is the
ability to create image layers. These layers can be
thought of as separate transparent sheets attached
to the base image. By placing different elements of
the image on separate layers, those elements can
be worked on independently, without changing
the rest of the image. Material on a layer can be
used to totally block out the corresponding image
area on layers below it, or may be decreased in
opacity to allow the underlying material to show
through to a greater or less degree. Layers can be
blended together for various effects, including
overall darkening or lightening of the image. This
blending technique is often used to bring out
detail in an overexposed (too light) image.
When an image from a scanner, digital
camera, or CD is first opened in the image editing
program, the image will be on a single layer
called the
Background
Layer. If only the common
digital darkroom tasks are to be performed on
the image, the single background layer may be
sufficient. (As noted earlier, you should make
a copy of the image and use that copy to make
changes. This preserves the original in its
unchanged state for future use, if necessary.)
Figure 15-13. You can use the
Canvas Size
dialog to
increase the space around your image. Open it by
clicking
Image Canvas
Size.
Figure 15-14. To increase the canvas size by a specific
amount, check the
Relative
box, then enter the desired
increase in width and height.