Network Working Group                                         S. Leonard
Internet-Draft                                             Penango, Inc.
Intended Status: Informational                          October 23, 2014
Expires: April 26, 2015

                     The Windows Bitmap Media Type


   This document registers the image/bmp media type for use with the
   Windows Bitmap format (BMP), also known as Device-Independent Bitmap
   (DIB). Originally designed for Microsoft Windows 2.0 and OS/2, these
   bitmaps contain a single raster graphic in a variety of compressed or
   uncompressed formats.

Status of this Memo

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1. Introduction

   Long before the invention of Portable Network Graphics (PNG),
   Microsoft Corporation and IBM Corporation needed to record images in
   a format that their applications and operating systems could easily
   render on low-end machines (Intel 80286). The resulting "BMP" format
   contains a single raster graphic with basic header fields that can be
   easily mapped (or "blitted") to locations in memory. As computing
   moved from 16-bit to 32-bit, BMP evolved to contain 32-bit
   structures. As the 90s wore on, the venerable BMP got boosts with
   support for additional color spaces, color profiles, and compression
   formats. The same basic format can be used to convey 2-bit black-and-
   white bitmaps with a 1-bit alpha mask from the '80s, and full-color
   Ultra HD images on leading-edge displays. BMP is a building block of
   other formats, including Windows Metafiles, Windows Icons, and
   Windows Cursors.

   Many implementations of BMP were created because of Windows'
   commercial success in the 1990s. Usage of the format for interchange
   has [[probably?]] declined since the advent of PNG (for lossless
   raster graphics) and JPEG (for lossy raster graphics); however, a
   large body of free and commercially available BMP artwork exists.
   Since Windows Icons are a building block of "favicon.ico" Web
   technology, an implementer would almost certainly need to support
   this format for basic interoperability.

   Microsoft publicly documented the BMP format as early as the 1992
   Windows 3.1 SDK (in the Windows Metafile documentation). Since 2007
   Microsoft has released the format specification [MS-WMF], which
   includes most components of the Windows Bitmap format, under its Open
   Specification Promise [MS-OSP]. See Section of [MS-WMF]
   (DeviceIndependentBitmap Object). BMP data begins with a
   BITMAPFILEHEADER and is followed by one of the bitmap headers
   table data, bitmap data, and optional profile data, in that order

   [[TODO: Maybe it is worth considering registering Windows cursors,
   animated cursors, and (re-registering) icons.]]

   The key word "SHOULD" in this document is to be interpreted as
   described in [RFC2119].

3. Windows Bitmap Media Type Registration Application

   Type name: image

   Subtype name: bmp

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   Required parameters: None.

   Optional parameters: None.

   Encoding considerations: Binary.

   Security considerations:

     Bitmaps have a mostly unremarkable security history.

     Because BMP data can encapsulate JPEG or PNG data (BI_JPEG, BI_PNG
     values of the Compression enumeration in Section of [MS-
     WMF]), the security considerations of JPEG and PNG processing may
     also apply to BMP.

   Interoperability considerations:

     Uncompressed Windows Bitmaps can be rather large. If there is a
     need to compress an image, modern applications SHOULD consider
     emitting JPEG or PNG data instead of embedding them in BMP

   Published specification: [MS-WMF] and [BMPSTOR].

   Applications that use this media type:

     Office productivity applications; clip art applications; desktop
     publishing applications; Web browsers; graphics processing

   Fragment identifier considerations: None.

   Additional information:

     Magic number(s): 42 4D ("BM"), meaning "bitmap". The next
                      field (BITMAPFILEHEADER bfSize) is a
                      little-endian DWORD indicating the size
                      of the bitmap content in bytes.
     File extension(s): .bmp, .dib
     Macintosh file type code(s):
       "BMP ", "BMPf", or "BMPp". Apple has promulgated a
       uniform type identifier (UTI) of "".

   Person & email address to contact for further information:

     Sean Leonard <>

   Restrictions on usage: None.

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   Author/Change controller: Sean Leonard <>

   Intended usage: COMMON

   Provisional registration? No

3.  IANA Considerations

   IANA is asked to register the media type image/bmp in the Standards
   tree using the application provided in Section 2 of this document.

4. Security Considerations

   See the registration template for security considerations.

6. References

6.1. Normative References

   [BMPSTOR]  Microsoft Corporation, "Bitmap Storage",
              MSDN ID dd183391, 2014,

   [MS-WMF]   Microsoft Corporation, "Windows Metafile Format",
              [MS-WMF], v20140502 (Rev 11.1), May 2014,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13, RFC
              6838, January 2013.

6.2. Informative References

   [MS-OSP]   Microsoft Corporation, "Open Specification Promise",
              February 2007,

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Author's Address

   Sean Leonard
   Penango, Inc.
   5900 Wilshire Boulevard
   21st Floor
   Los Angeles, CA  90036


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