Using Layers; About Layers - Adobe PHOTOSHOP 6.0 Manual

Chapter 8: Using Layers
W hen you create, import, or scan an
image in Adobe Photoshop or
Adobe ImageReady, the image consists
of a single layer. You can add more layers to the
image, allowing you to organize your work into
distinct levels.

About layers

A new image in Photoshop or ImageReady has a
single layer. In Photoshop, this layer is called the
background layer and is analogous to the base layer
of a painting. You cannot change the position of
the background layer in the stacking order (it is
always at the bottom of the stacking order); nor
can you apply a blending mode or opacity to a
background layer (unless you first convert it to a
normal layer).
Layers allow you to make changes to an image
without altering your original image data.
For example, you might store photographs or
elements of photographs on separate layers and
then combine them into one composite image.
Think of layers as sheets of acetate stacked one on
top of the other. Where there is no image on a layer
(that is, in places where the layer is transparent),
you can see through to the layers below. All layers
in a file have the same resolution, start with the
same number of channels, and have the same
image mode (RGB, CMYK, or Grayscale).
The zebra is on the topmost layer.
Transparent areas on a layer let you see through
to the layers below.
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