PDF (adobe.com)

Save a file in GIF format

You can use the Save As command to save RGB, Indexed Color, Grayscale, or Bitmap mode images directly in CompuServe GIF (known as GIF) format. The image is automatically converted to Indexed Color mode.
Note: GIF is only available when the image is 8 Bits/Channel (it only supports 8 Bit/Channel).
  1. Choose File > Save As, and choose CompuServe GIF from the Format menu.
  2. For RGB images, the Indexed Color dialog box appears. Specify conversion options and click OK.
  3. Select a row order for the GIF file, and click OK:
    Normal
    Displays the image in a browser only when download is complete.

    Interlaced
    Displays low-resolution versions of the image in a browser as the file downloads. Interlacing makes download time seem shorter, but it also increases file size.
    Note: You can also save an image as one or more GIF files using the Save For Web & Devices command.