Sun Rasterfile Format
from the man pages : 
rasterfile(4)             File Formats              rasterfile(4)

NAME
     rasterfile - Sun's file format for raster images

SYNOPSIS
     #include <rasterfile.h>

DESCRIPTION
     A rasterfile is composed of three parts:   first,  a  header
     containing  8  integers;  second,  a (possibly empty) set of
     colormap values; and third, the pixel image, stored  a  line
     at a time, in increasing y order.  The image is layed out in
     the file as in a memory pixrect.  Each line of the image  is
     rounded up to the nearest 16 bits.

     The header is defined by the following structure:

          struct rasterfile {
               int  ras_magic;
               int  ras_width;
               int  ras_height;
               int  ras_depth;
               int  ras_length;
               int  ras_type;
               int  ras_maptype;
               int  ras_maplength;
          };

     The ras_magic field always contains the following constant:

          #define   RAS_MAGIC 0x59a66a95

     The ras_width, ras_height, and ras_depth fields contain  the
     image's  width  and  height in pixels, and its depth in bits
     per pixel, respectively.   The  depth  is  either  1  or  8,
     corresponding   to   standard   frame  buffer  depths.   The
     ras_length field contains the length in bytes of  the  image
     data.   For  an  unencoded  image, this number is computable
     from the ras_width, ras_height, and  ras_depth  fields,  but
     for  an  encoded image it must be explicitly stored in order
     to be available without decoding the  image  itself.   Note:
     the  length of the header and of the (possibly empty) color-
     map values are not included in the value of  the  ras_length
     field;  it  is  only  the image data length.  For historical
     reasons, files of type RT_OLD will usually have a 0  in  the
     ras_length  field,  and software expecting to encounter such
     files should be prepared to compute the  actual  image  data
     length  if needed.  The ras_maptype and ras_maplength fields
     contain the type and length in bytes of the colormap values,
     respectively.   If  ras_maptype  is  not  RMT_NONE  and  the
     ras_maplength is not 0, then the  colormap  values  are  the
     ras_maplength  bytes  immediately  after  the header.  These
     values are either  uninterpreted  bytes  (usually  with  the
     ras_maptype  set  to RMT_RAW) or the equal length red, green
     and blue vectors, in that order  (when  the  ras_maptype  is
     RMT_EQUAL_RGB).  In  the latter case, the ras_maplength must
     be three times the size in bytes of any one of the vectors.

SunOS 5.4          Last change: 29 March 1994
Here is an additional note found in the newsgroups :
			Inside SUN Rasterfile
			    Jamie Zawinski
			jwz@teak.berkeley.edu

The manpage for rasterfile(5) doesn't say anything about the format of
byte-encoded images, or  about plane/scanline  ordering in multi-plane
images.

The first thing in the file is

	struct rasterfile {
		int ras_magic;
		int ras_width;
		int ras_height;
		int ras_depth;
		int ras_length;
		int ras_type;
		int ras_maptype;
		int ras_maplength;
		};

The ras_magic field always contains the following constant:

	#define RAS_MAGIC 0x59a66a95

The ras_length field  is the  length of the image  data (which  is the
length of  the file minus   the  length  of the header  and colormap).
Catch: this is sometimes zero  instead, so you  can't really depend on
it.

The ras_type  field is  ras_old=0, ras_standard=1, ras_byte_encoded=2,
or  ras_experimental=FFFF.  There  doesn't seem to   be any difference
between OLD and STANDARD except that the ras_length  field is always 0
in OLD.

I didn't deal with cmaps, so from the  man page: "The  ras_maptype and
ras_maplength  fields contain  the type and   length in   bytes of the
colormap values, respectively.  If ras_maptype is not RMT_NONE and the
ras_maplength is not 0, then the colormap values are the ras_maplength
bytes    immediately  after  the   header.   These   values are either
uninterpreted bytes (usually  with the ras_maptype  set to RMT_RAW) or
the equal length red, green and blue vectors, in  that order (when the
ras_maptype is RMT_EQUAL_RGB).  In the  latter case, the ras_maplength
must be three  times the size  in bytes of  any  one of the  vectors."
Regardless of width, the stored scanlines are  rounded up to multiples
of 16 bits.

I found the following description of byte-length encoding in Sun-Spots
Digest, Volume 6, Issue 84:

The format is composed of many sequences of variable length records.
Each record may be 1, 2, or 3 bytes long.

 o  If the first byte is not 0x80, the record is one byte long, and 
    contains a pixel value.  Output 1 pixel of that value.
 o  If the first byte is 0x80 and the second byte is zero, the record
    is two bytes long.  Output 1 pixel with value 0x80.
 o  If the first byte is 0x80, and the second byte is not zero, the 
    record is three bytes long.  The second byte is a count and the 
    third byte is a value.  Output (count+1) pixels of that value.

A run is not terminated at the end of a scan line.  So, if there are 
three lines of red in a picture 100 pixels wide, the first run will 
be 0x80 0xff 0x<red>, and the second will be 0x80 0x2b 0x<red>. 
 
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