Information for type creators

Embedding TrueType

The solution to document portability
Making documents truly portable from one user's computer to another is complicated because fonts used in the document by the author might not be installed on the reader's machine.
    Strategies for overcoming this range from synthesizing the fonts on the user's system (by extrapolating elements of one or two fonts to simulate the required size and shape) to copying only certain aspects of a font, in a bid to reduce the file size of the information required. But document quality always suffers.
    The World Wide Web has focused attention on these issues. Web site designers and authors need to have control over the appearance of their pages on users' browsers.

What is font embedding?
Font embedding is a method of including fonts with the documents in which they are used. By embedding a font with a document, authors and designers are able to ensure that their text will appear correctly on other users' systems, even if that system doesn't possess the correct fonts. Because the fonts are included with the actual document, the user's operating system and application or viewer is able to access the embedded fonts and to make use of them. In contrast with only copying selected elements of a font, embedding the font involves sending the real font, with all of its original high quality outlines, metrics and hinting information. Font embedding is thus the only way to ensure that a text will appear exactly the way it was intended.

Why is embedding necessary?
Without the correct fonts, the document will not display correctly, and default or synthesized fonts will be used instead. This will affect the appearance of the document in three ways:
    First, the aesthetic quality of the document is affected. Synthesized substitutes cannot compete with the high quality outlines, spacing and hinting of the real font. Italicized and emboldened variants of the font will not be true variants, but 'pseudo' altered versions of the same font. Embedding fonts, on the other hand, results in a higher visual quality because the font retains its integrity and uses the information the font was originally, and carefully, designed with.
    Second, the spacing and formatting of the document can be drastically altered. The original font may be replaced with another font having different metrics, widths and spacing, resulting in text reflow when the text is scaled or printed. Over a long document this can substantially alter the number of pages in a document. Font embedding ensures that the correct character metrics (widths, sizes and spacing) are retained and used.
    Finally, it is impossible for a synthesizing method to synthesize unique and odd display faces, and also to produce characters from character sets not included in the base fonts. Embedding fonts ensures that exactly those characters that are needed are included.
    Because font embedding enables the user to send correct, high-quality character outlines, metrics and correct character mapping information, authors can guarantee that their documents and files will appear exactly as they intended them to.

Considerations
Standard licensing policy allows a font to be used by only one (machine or user). The user cannot give the font to recipients of the document. Font embedding, on the other hand, ties the font to the document, and not to the user. Through standards set up in consultations between Microsoft and the font industry, TrueType fonts contain permissions (determined by the original creator of the font) which allow the font to travel with the document under certain restrictions:

• Fully installable means that the font contained in the document can be installed on the recipient's machine and used without restriction in other applications.
• Editable fonts can be used to make changes to the document in which the font is embedded, but cannot be used elsewhere.
• Print preview allows the document to be viewed on screen and printed, but the font cannot be used in other applications or for changing the document as it is received.
• Do not embed is used by font creators who do not wish the font to travel with any document.

Subsetting reduces file size
Because a document rarely uses all of the characters contained in a font, the size of the document can be reduced by subsetting the font. Subsetting allows only the characters used in a text to be sent with the document. Many English language documents, for example, seldom include the Greek characters often found in fonts, and so would not require these characters to be sent with the document. Subsetting a font does mean that the font is no longer editable by the recipient.

How font embedding works
In order for a document to use font embedding, the application that creates and reads the document must support font embedding. When the document is saved, the user is usually given the option to embed the fonts in the document. The illustration below shows how Microsoft PowerPoint offers the user this option at the File Save stage:

At this point, the application determines which fonts are used in the document, and associates an encrypted version of the font with the document. If a font does not allow embedding, it is not placed in the document. When this document is read on the recipient's machine, the fonts are unencrypted. If the font is fully installable, the font is installed on the recipient's machine. Otherwise, the font is installed so that no other applications can see or use the font. In the 'print and preview' case, the document is set to read-only, so that no modifications can be made to it. When the user is finished with the document, the fonts are uninstalled from the system, except in the case of fully-installable fonts.

Technical specifications and information on embedding will be made available here shortly. In the meantime, font and software developers requiring information on implementing TrueType embedding can send e-mail to ttfaq@microsoft.com

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this document last updated 10 March 1996
content copyright © 1996 Microsoft Corporation. all rights reserved
comments to the MST group: ttwsite@microsoft.com