Network Working Group
Request for Comments: 797
A. Katz
September 1981


   This note describes a proposed format for storing simple bitmaps (one
   bit per pixel)  in a file.   These  files  may be very  large and the
   intent  is to use this format for short term storage and passing data
   between  closely  coupled  programs.   The data in the file should be
   stored in 8-bit bytes (octets).  Bitmaps may be any size.
   The first  4 octets  of the file  gives  the width  of each  line  (x
   direction),  and the next 4 octets should give the number of lines of
   the display  (length, y direction). After this is one octet for the x
   increment  and one octet for the y  increment.   Following  these  10
   octets  is the bitmap  itself.     The length  and width  fields  are
   stored most significant octet first.
   The x and y increment  octets  tell how much space is between pixels.
   For an ordinary display, both these would be one.
   Each line of the display  should  be scanned  from left to right. The
   lines should start at the top and work down.  Each line in the bitmap
   should  end on an octet boundary.  If the width of the display is not
   divisable  by 8,  the rest of the last octet  should  be filled  with
   zeros on the right.
   Below  is a representation  of a bitmap  file  (each  square  is  one
      |    1     |    2     |    3     |     4     |     5     |
      |  width   |  width   |  width   |   width   |  length   |
      |     6    |     7    |     8    |     9     |     10    |
      |  length  |  length  |  length  |x-increment|y-increment|
      |   11     |   12     |   13     |    14     |   15
      |  data    |  data    |  data    |   data    |  data...
   For example,  bitmaps  from the RAPICOM  450 can be in  Fine  Detail,
   Quality,  or Express  Mode.   In Fine Detail mode the x-increment and
   y-increment  would be 1, for Quality mode, the x-increment would be 1
   and the y-increment would be 2, and for Express mode, the x-increment
   would  be 1 and the y-increment  would be 3.  For these bitmaps it is
   intended  that each scan line be repeated y-increment times when they
   are displayed.