Technical data

Using Layers and Masks 61
Layers
If you’re accustomed to thinking of pictures as flat illustrations in
books, or photographic prints, the concept of image layers may take
some getting used to. In fact, layers are hardly unique to electronic
images. The emulsion of photographic film has separate layers, each
sensitive to a different color—and we’ve all noticed multiple-image
depth effects like shop window reflections or mirrored interiors. There
is still something magical about being able to build up an image in a
series of planes, like sheets of electronic glass, each of which can vary
in transparency and interact with the layers below to produce exciting
new images and colors.
Kinds of layers
In a typical PhotoPlus image—for
example, a photograph you’ve scanned in,
a new picture file you’ve just created, or a
standard bitmap file you’ve opened—there
is one layer that behaves like a
conventional “flat” image. This is called
the Background layer, and you can think
of it as having paint overlaid on an
opaque, solid color surface.
You can create any number of new layers in your image. Each new one
appears on top of the rest, comprising a stack of layers that you can
view and manipulate with the Layer Manager tab. We call these
additional layers standard layers to differentiate them from the
Background layer. Standard layers behave like transparent sheets
through which the underlying layers are visible.
Then there are text layers, which are essentially standard layers but
much more limited—their main job is to hold blocks of text separately
from the other layers so that the text remains editable.
A key distinction is that pixels on the Background layer, once laid
down, are fully opaque, while those on standard layers can vary in
opacity (or transparency, which is really the same thing). That’s
because standard layers have a “master” Opacity setting that you can
change at any time, while the Background layer does not. A couple of
examples will show how this rule is applied in PhotoPlus: