深入解析：微软EMF文件格式与实现授权

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本文将深入解析微软的Enhanced Metafile Format (EMF) 文件格式，这是一种专为Windows操作系统设计的矢量图形文件格式，主要用于在应用程序中高效地存储和传输图形数据。EMF 文件格式由 Microsoft Corporation 提供，版本更新至2010年11月12日，其版权信息表明该文档属于开放规格说明书的一部分，允许开发者根据这些规范进行实施和复制。在 EMF 格式中，Microsoft 的目标是为协议、文件格式、语言、标准以及技术间交互提供详细的概述，以便于开发人员理解和利用。版权方面，用户可以在遵守文档中包含的使用条款前提下，复制该文档以开发基于 EMF 技术的产品，并在必要时分发部分文档或代码示例，包括随文档提供的schema、IDL（接口定义语言）和代码片段，无论是否进行修改。同时，引用的任何其他文档也受到相同的许可。 EMF 文件格式具有以下关键特性： 1. **矢量图形表示**：EMF 采用矢量数据结构来表示图像，这意味着它不依赖分辨率，因此即使放大或缩放，图像质量也能保持一致，适用于高质量打印和高分辨率显示。 2. **平台独立性**：尽管与Windows平台紧密相关，但通过跨平台库或工具，EMF 图像可以被移植到其他环境，支持不同操作系统上的应用程序。 3. **高效性能**：由于数据是基于几何形状和颜色信息，而非像素，处理复杂图形时比位图（如BMP或JPEG）更快且占用更少的存储空间。 4. **可扩展性和兼容性**：EMF 可以嵌套在其他EMF文件中，便于创建更复杂的图形结构。同时，许多应用程序能直接处理EMF，使得它成为一种通用的图形交换格式。 5. **元数据支持**：EMF 文件不仅可以包含图形内容，还能包含有关图形的额外信息，如线条样式、字体和颜色等，方便后期编辑或自动化处理。理解 EMF 格式对于开发Windows应用、图形处理软件以及需要高效图形表现的开发者来说至关重要。掌握这一格式，开发者能够创建出兼容广泛、性能优越的应用程序，同时确保知识产权的合规使用。

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1.2 References

1.2.1 Normative References

We conduct frequent surveys of the normative references to assure their continued availability. If

you have any issue with finding a normative reference, please contact dochelp@microsoft.com. We

will assist you in finding the relevant information. Please check the archive site,

http://msdn2.microsoft.com/en-us/library/E4BD6494-06AD-4aed-9823-445E921C9624, as an

additional source.

[ISO/IEC-8859-1] International Organization for Standardization, "Information Technology -- 8-Bit

Single-Byte Coded Graphic Character Sets -- Part 1: Latin Alphabet No. 1", ISO/IEC 8859-1, 1998,

http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=28245&ICS1=35&ICS

2=40&ICS3=

Note There is a charge to download the specification.

[JFIF] Hamilton, E., "JPEG File Interchange Format, Version 1.02", September 1992,

http://www.w3.org/Graphics/JPEG/jfif.txt

[MS-WMF] Microsoft Corporation, "Windows Metafile Format", June 2007.

[RFC2083] Boutell, T., "PNG (Portable Network Graphics) Specification Version 1.0", RFC 2083,

March 1997, http://www.ietf.org/rfc/rfc2083.txt

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

2119, March 1997, http://www.ietf.org/rfc/rfc2119.txt

[UNICODE] The Unicode Consortium, "Unicode Home Page", 2006, http://www.unicode.org/

1.2.2 Informative References

[MS-EMFPLUS] Microsoft Corporation, "Enhanced Metafile Format Plus Extensions", June 2007.

[MS-EMFSPOOL] Microsoft Corporation, "Enhanced Metafile Spool Format", June 2007.

[MS-GLOS] Microsoft Corporation, "Windows Protocols Master Glossary", March 2007.

[MSDN-GDI+] Microsoft Corporation, "GDI+", http://msdn.microsoft.com/en-

us/library/ms533798.aspx

[MSDN-WRLDPGSPC] Microsoft Corporation, "World-Space to Page-Space Transformations",

http://msdn.microsoft.com/en-us/library/ms532657.aspx

[OPENGL] Segal, M. and Akeley, K., "The OpenGL Graphics System: A Specification, Version 2.1",

December 2006, http://www.opengl.org/registry/doc/glspec21.20061201.pdf

1.3 Overview

1.3.1 Metafile Structure

The EMF specifies a collection of data records that contain graphics drawing commands and object

definitions. EMF metafiles provide true device independence; the image defined in an EMF metafile

maintains its dimensions, shape, and proportions on any output device, including printers, plotters,

desktops, and in the client areas of many applications.

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Figure 1: EMF metafile structures

Thus, all EMF metafiles can be considered to have three sections:

EMF Header: The metafile header with extensions that correspond to this type of EMF metafile.

The header record contains information concerning the structure and contents of the metafile,

including an optional description string and pixel format descriptor. See section 2.3.4.2 for details

concerning the EMF header.

EMF Records: An array of EMF records that contains drawing orders, graphics state information,

and graphics object definitions. At least one record has to be present—not counting the EMF

header or EMF end-of-file records—or the metafile is invalid. See sections 2.3.10 and 2.3.5 for

specifications of all EMF record types.

EMF End-of-File: The EMF end-of-file record signals the end of all EMF metafiles. It has to be

the last record in the metafile. If the EMF metafile contains an optional palette, it is in the form

of an array of LogPaletteEntry (section 2.2.18) objects located in the EMF end-of-file record.

Offsets to the palette are present in both the EMF header and EMF end-of-file records.

Within the portions of these files identified as EMF header records, the description and pixel format

substructures are optional, and they can be placed in any order. Their presence, location, and

relative order in a given EMF file are determined by offset values in the EMF header record. If

present, they are part of the EMF header record, and cannot be located at some arbitrary location in

the EMF metafile, such as between EMF records.

EMF records are contiguous; this is required, because the information that is available for traversing

the file from record to record depends on it. That is, from any given EMF record, including the

header record, in order to move to the next sequential record in the file, the length of the record is

used.

1.3.2 Graphics Objects

Graphics objects, which are used in the drawing and painting operations specified in the records of

an EMF metafile, are created by Object Creation record types, specified in section 2.3.7, prior to the

records that specify their use. These objects are designed to be reusable during the course of

processing the EMF metafile.

Throughout this specification, it is assumed that these previously defined, reusable graphics objects

are available when needed for the processing of particular metafile records. This store of available

objects is referred to in the text as the EMF Object Table, which is described in section 3.1.1.1. The

exact characteristics of an object store for EMF objects can be determined by the particular

implementation that parses or writes EMF metafiles.

The types of reusable objects that can be created and managed during EMF metafile playback

include:

Brushes, specified in section 2.2.12

Color spaces, specified in [MS-WMF] sections 2.2.2.11 and 2.2.2.12

Fonts, specified in sections 2.2.13, 2.2.14, 2.2.15, and 2.2.16

Palettes, specified in section 2.2.17

Pens, specified in sections 2.2.19 and 2.2.20

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When one of these objects is created, it is assigned a 32-bit index in the EMF Object Table. An

object can be "activated" by an EMR_SELECTOBJECT record that refers to the index it was assigned.

There are also stock objects that can be selected for use in graphics operations. Stock objects are

also assigned 32-bit indexes, but not at run time—their indexes are predefined. They are

distinguished from the indexes of dynamically created graphics objects by having the most-

significant bit set to 1. The other 31 bits of the index define the particular stock object, according to

the StockObject enumeration, specified in section 2.1.31.

1.3.3 Byte Ordering

Data in metafile records is stored in little-endian format.

Some computer architectures number bytes in a binary word from left to right, which is referred to

as big-endian. The byte numbering used for bitfields in this specification is big-endian. Other

architectures number the bytes in a binary word from right to left, which is referred to as little-

endian. The byte numbering used for enumerations, objects, and records in this specification is

little-endian.

Using the big-endian and little-endian methods, the number 0x12345678 would be stored as shown

in the following table.

Byte order

Byte 0

Byte 1

Byte 2

Byte 3

Big-endian

0x12

0x34

0x56

0x78

Little-endian

0x78

0x56

0x34

0x12

1.4 Relationship to Protocols and Other Structures

EMF is related to the following file formats:

Windows metafile format (WMF) [MS-WMF] uses similar graphics, commands, and objects,

but WMF files are not device-independent.<5>

Enhanced metafile spool format (EMFSPOOL) [MS-EMFSPOOL] is an application of EMF for

print job spooling.

Enhanced metafile format plus extensions (EMF+) [MS-EMFPLUS] specifies object-oriented

structures that can be embedded in EMF metafiles.<6>

1.5 Applicability Statement

Files that adhere to the EMF metafile format can be used as portable, device-independent containers

for images. The graphics supported in EMF metafiles are applicable to document content

representation, including printing and plotting.

1.6 Versioning and Localization

This specification covers versioning issues in the following areas:

Versioning: The EMF structure has been revised twice. The different versions are:

Original: The first version of the EMF structure, supporting records that define drawing

commands and graphics objects.

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