PDF (adobe.com)

Define an image as a preset pattern

  1. Use the Rectangle Marquee tool  on any open image to select an area to use as a pattern. Feather must be set to 0 pixels. Note that large images may become unwieldy.
  2. Choose Edit > Define Pattern.
  3. Enter a name for the pattern in the Pattern Name dialog box.
    Note: If you are using a pattern from one image and applying it to another, Photoshop converts the color mode.
    Photoshop comes with a set of Illustrator format files that you can use to define a preset pattern. Open the file, select any rendering option, and then define the pattern.