Information for type users

Introduction to TrueType

It is important to understand why TrueType exists at all. TrueType was created as an alternative (open standard) scaleable digital type to compete with Adobe PostScript Type 1 fonts.

Two of the aims in creating TrueType were: to encapsulate the existing type technologies (Adobe Type 1, Agfa Intellifont, Bitstream Speedo, Nimbus Q etc); and to improve on the existing technologies.
    As the world becomes more electronic, we read more and more words on television and computer screens, or printed on medium resolution office printers. Electronically generated documents have many obvious advantages, but they also have a few problems.
    One of them is the legibility of type at small sizes, especially on a computer screen.
    Computers originally used simple character bitmaps to form words. Because you had to have a screen bitmap font for each point size you might need, and also needed an equivalent bitmap font for each different type of printer, you used a lot of memory. You couldn't use screen bitmaps on a laser printer because they would print out at low resolution, and result in very poor looking documents.

Figure 1 Using screen-size bitmaps on a printer, and enlarging a bitmap of a particular size, resulted in poor looking text.

The next step (after bitmaps) in the development of digital type was to use scaleable outlines. Each character is stored as a mathematical outline, and need only be stored once, instead of once for each size and output device like bitmaps. When you ask for a certain size (eg 24pt) the outlines are scaled to that size, and used to generate a bitmap.

Figure 2 & Figure 3 Scaling the outline of this W, and the bitmaps it generates, clearly shows how much easier it is to represent that W as more pixels become available.

This was a great leap forward, and the credit goes to Adobe Systems Inc., who popularized PostScript® Type 1 fonts. This advance allowed the use of a much broader range of point sizes, and let printers produce great-looking documents. The beauty of this system is that when you scale the outline you can lay it over either the grid (72dpi or 96dpi) that represents your screen, or the grid that represents the printer you are using at the time (office printers being typically 300 to 600dpi).

Figure 4 Although these W's are the same size, the one on the right is clearer because of the much greater number of pixels available to describe the shape at the higher resolution.

As usual, with every step forward, a few more problems are encountered and need to be solved. For example, at certain resolutions the method used to fill an outline may not turn on a very suitable set of pixels to represent the character that you want to display.

Figure 5 This is what happens when we turn on only the pixels that fall entirely within the outline, resulting here in a great deal of missing information in the character shape.

Figure 6 There are alternatives. We could turn on all the pixels that have any part within the outline, creating a very bold character.

Figure 7 Another option is to turn on only the pixels that have more than 50% within the outline. In this instance, the left arch loses detail and one of the stems becomes thin.

As you can see, all of these produce far from ideal results. This is not a problem if you are printing to high resolution imagesetters, but it is a top priority if you want to make type legible at the low resolutions at which we read most text in business and on-line documents.
    The solution to this problem is called hinting. Hinting is influencing which pixels get turned on, in order to create the best possible bitmap using the available resolution. Ideally you might hint the 'm' so that it looks like the one below.

Figure 8 A well hinted letter 'm' where all the pixels have been carefully chosen.

Although PostScript® has some hinting facilities, these hints consist mostly of a few global parameters that do part of the job, but by no means all of it. TrueType technology, however, is designed to give the type designer a huge degree of control over how each bitmap and character space turns out at each point size. It has also overcome the need for separate screen fonts. Instead, the fonts are self-contained and easy to install.
    With the power to control the character shapes so carefully, TrueType brings back the fine control that type designers had in the past. Traditionally, smaller point sizes of a typeface were quite different from the larger sizes in a number of ways. For example, the characters at smaller sizes become wider and heavier, and the letter spacing increases.

TrueType allows us to implement the rules that printers and type designers have spent centuries learning, and apply them in the most modern of contexts - the computer screen - where they have once again become so important.

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

Adobe is a trademark of Adobe Systems, Inc
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PostScript is a trademark of Adobe Systems, Inc
TrueType is a registered trademark of Apple Computer, Inc