Type: Bitmap and animation
    Extension: .ANI, .ANM, .CE?, .FLM, .NEO, .PAC, .PC?,
               .PI?, .RGB, .SEQ, .TNY, .TN?, .UC?
      Version: Variuos
  Compression: None, RLE
  Color Depth:
   Maintainer: 
Specification:

The primary graphics file format of the Atari ST system is the
Electronic Arts Interchange File Format (IFF).  However, a collection
of poorly documented image file formats native to the Atari ST
computer do exist as well. These formats are used primarily for
storing still-images, animations, and screen dumps. 

The Computer Eyes Raw Data Format (.CE1, .CE2), Imagic File/Picture
Format (.IC1, .IC2, .IC3), NEOchrome Format (.NEO), RGB Intermediate
Format (.RGB), STAD Format (.PAC), Tiny Format (.TNY, .TN1, .TN2,
.TN3) are bitmap file formats. The Animatic File Format (.ANM), Cyber
Paint Sequence Format (.SEQ), DEGAS Format (.PI1, PI2, .PI3, .PC1,
.PC2, .PC3), and NEOchrome Animation Format (.ANI) are animation file
formats.

There seems to be no official documentation for most of these
formats. The document, "Atari ST Picture Formats", by David M.
Baggett <dmb@ai.mit.edu> does seem to be the definitive reference.
You can find it at:

  ftp://atari.archive.umich.edu/.../picfmts.doc

You may also find information on Atari ST formats on the
comp.sys.atari.st Usenet newsgroup, and on the following Web sites:

  Dan's Atari ST Web Pages
  http://newton.ex.ac.uk/general/ug/jones/

  Atari ST FAQ
  http://www.smartpages.com/faqs/csas-faq/top.html