Windows Metafile
| Filename extension | |
|---|---|
| Internet media type | image/wmf, image/emf |
| Developed by | Microsoft |
| Initial release | 1990 |
| Latest release |
12
(30 June 2015) |
| Type of format | Image file formats |
| Container for | Bitmaps among others |
| Open format? | Microsoft OSP |
Windows Metafile (WMF) is an image file format originally designed for Microsoft Windows in the 1990s. Windows Metafiles are intended to be portable between applications and may contain both vector graphics and bitmap components. It acts in a similar manner to SVG files.
Essentially, a WMF file stores a list of function calls that have to be issued to the Windows Graphics Device Interface (GDI) layer to display an image on screen. Since some GDI functions accept pointers to callback functions for error handling, a WMF file may erroneously include executable code.
WMF is a 16-bit format introduced in Windows 3.0. It is the native vector format for Microsoft Office applications such as Word, PowerPoint, and Publisher. As of 2015[update] revision 12 of the Windows Metafile Format specification is available for online reading or download as PDF.
The original 16 bit WMF file format was fully specified in volume 4 of the 1992 Windows 3.1 SDK documentation (at least if combined with the descriptions of the individual functions and structures in the other volumes), but that specification was vague about a few details. These manuals were published as printed books available in bookstores with no click through EULA or other unusual licensing restrictions (just a general warning that if purchased as part of a software bundle, the software would be subject to one).
Over time the existence of that historic specification was largely forgotten and some alternative implementations resorted to reverse engineering to figure out the file format from existing WMF files, which was difficult and error prone. In September 2006, Microsoft again published the WMF file format specification in the context of the Microsoft Open Specification Promise, promising to not assert patent rights to file format implementors.
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