RFC797 - Format for Bitmap files

王朝other·作者佚名 2008-05-31

Network Working Group A. Katz

Request for Comments: 797 ISI

September 1981

FORMAT FOR BITMAP FILES

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

octet):

----------------------------------------------------------

1 2 3 4 5

width width width width length

----------------------------------------------------------

6 7 8 9 10

length length length x-incrementy-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

Alan R. Katz [page 1]

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.

[page 2] Alan R. Katz