Analysts and experts are predicting big things for ITV. The market is still in its infancy, and much needs to be done before ITV set-top boxes (STBs) are in every household. One thing is clear: the ability to quickly generate high-quality text, fine-tuned for TV screens, will be a key ingredient in the success of ITV--an ingredient that Bitstream, with its TrueDoc technology, is ideally positioned to deliver.

When all these services and capabilities are delivered at a reasonable price, the STB will be an application that everyone is seeking to turn TVs into a two-way interactive vending and communication machine.

Figure 1. Set-top box architecture for a typical implementation.
Bitmap fonts stored in ROM allow for display of non-interactive text.

A set-top box delivering all these services would rival or even exceed the processing capability and speed of a typical personal computer. However, to win widespread acceptance, developers must keep the cost of goods low.

Developers are working on new microprocessors, new operating systems, and new computing models. To keep the cost of goods low, hardware manufacturers cannot provide the fastest processors available or large amounts of ROM and RAM. Working within a memory-starved environment, set-top boxes will have to quickly deliver high-quality multimedia (text, graphics, video, animation, sound) or risk losing the attention of the general public.

The Market Need
As with computers, set-top boxes require an operating system. To generate text, the operating system needs to incorporate a font subsystem, which consists of a core set of fonts and a font rasterizer. (By way of comparison, the Windows operating system includes a core set of TrueType fonts and the TrueType font rasterizer.)

Text generation will be a key component in providing true, interactive multimedia for customers. Text generation requires fonts. Early attempts to furnish STBs with resident fonts relied on stored bitmap fonts, but these require a lot of storage space and are limited to specific characters, sizes, and resolutions.

Bitmap font solutions were the only solution available until recently. Although bitmaps fonts provide high-quality characters at a specific size and resolution, you cannot use them to generate readable text at other sizes and resolutions. And to support different languages, you need something more than bitmaps. After all, you cannot hope to store characters in bitmap format for every language you need to support.

The Bottom Line:
To provide true interactive multimedia for a worldwide audience, set-top boxes must render high-quality text quickly, in any language, on the TV screen.

Business Plan
Bitstream's business plan is to offer TrueDoc as a software development kit (SDK). STB developers can use TrueDoc to provide all the type and type technology they need for a state-of-the-art character generation system. Bitstream's business model is simple. It involves an up-front access fee for the SDK, plus royalties for every unit sold. This business plan fits well with the needs of STB developers, who want to keep the price of each unit low.

About TrueDoc
Bitstream TrueDoc is a dynamic font scaler that can be built into embedded devices, such as printers, information appliances, and--now--set-top boxes and network computers. TrueDoc consists of two main components: the Character Shape Recorder (CSR) and the Character Shape Player (CSP). The TrueDoc CSR records character shapes (glyphs) and stores them in a highly compact data structure called a Portable Font Resource (PFR). PFR data can be embedded within A document or stored on a server. It can also be pre-built and stored in the ROM (read-only memory) of an embedded device. From the data in the PFR, TrueDoc's CSP renders the character shapes on the fly, delivering high-quality glyph images quickly.

How TrueDoc Works in ITV Applications
Developers can implement TrueDoc in a number of ways to suit both the immediate and long-term needs of the interactive television market.

The most basic implementation of TrueDoc for set-top boxes includes the TrueDoc Character Shape Player and a pre-built Portable Font Resource in ROM. The PFR can contain a variety of fonts, in a variety of languages, with any character set. This implementation works for generating text in electronic program guides (EPGs), displaying Web content, or allowing the consumer to input text.

Figure 2. Set-top box architecture for a TrueDoc-enhanced implementation.
Storing the PFR fonts and the CSP in ROM allows for the display of both static and dynamic text from a variety of sources, including multilingual documents.

Implementations for EPGs (electronic programming guides) require a small set of fonts that can be stored inside the set-top box. Some program guides you see on cable TV are non-interactive. They simply display the programs offered on different channels and the times the programs are shown. Effective electronic programming guides, on the other hand, are interactive and require a set-top box. You can use EPGs, for example, to set up an entire day's worth of programs, then record them on your VCR or DVR. Or you can use EPGs to scroll through a list of movies, then select a movie to see or even a preview of a movie. Either way, STBs put the control of content into the viewer's hands.

The TrueDoc CSP can quickly generate the characters that the EPG needs, render high-quality text, and fine tune it for display on the TV screen.

TrueDoc lets developers implement a truly interactive product. The STB can create and generate text on the fly, using fonts beyond those in the pre-built PFR in ROM.

Easy Implementation
Implementing TrueDoc is easy, compared with other embeddable, font scaling technologies. TrueDoc's SDK is modular, professionally documented, and extremely easy to use. The Application Programming Interface (API) is uncluttered. It looks and reads like a high-level text API, similar to the code that Windows and Macintosh engineers are used to seeing.

As a company that specializes in delivering source code to OEM (original equipment manufacturers) and ISV (international service vendors) customers, Bitstream has always provided code that is well-written, easy to work with, and well-documented.

High-Quality Output
TrueDoc PFRs contain intelligently-hinted, scalable outlines. To fine-tune text generation for TV screens, Bitstream enhanced the PFR hinting logic to create the most natural character shapes possible for standard televisions, which are low-resolution devices. Hinting involves fine tuning every character in a font so that it is at its most legible. Hints are instructions for particular characters at specific point sizes and resolutions that, for example, make sure there are no dropouts of pixels in the hairlines, stems, and serifs of a particular letterform when it is rendered at small point sizes on a screen. Bitstream has been refining hinting technology and techniques for over ten years.

TrueDoc produces well-formed characters regardless of output size or resolution. TrueDoc also contains other enhancements to ensure the highest-quality output on a variety of devices:

• Anti-aliased output
• Color blending and filtering
• Sub-pixel positioning

Bitstream has also developed a color blending scheme that works with its anti-aliasing. This produces the best possible output for text on backgrounds--for example, red text with a yellow drop shadow on a blue background. The CSP can smooth out character edges in both the x and y dimensions, using filters that average out color, such as that between red text and a yellow drop shadow, or between a yellow drop shadow and a blue background. The CSP controls these filters with "weighted ramps," which smooth out the transition from background to foreground color in a manner that suppresses such artifacts on TV screens as ghosts, flickers, and hot spots.

In addition, TrueDoc includes subpixel positioning. Subpixel positioning lets you more accurately compose lines of type for the screen. This results in better spacing between characters, even when text is rotated. Previously, outlines of character shapes were simply fitted to character grids on an output device (such as a laser printer or a computer screen). If a pixel fell within the outline of a character shape, the pixel was turned on. If not, the pixel was turned off.

With this new technology, the CSP can control the placement of a character down to one-sixteenth of a pixel. This solves the problems of legibility and readability that can occur when text is composed for a TV screen, which is a low-resolution device (compared to a computer monitor). Characters can be placed at subpixel positions of whole, half, quarter, eighth, and sixteenth pixels, both in the x and y dimensions. The TrueDoc CSP can thus adjust and control the placement of characters with an unparalleled degree of accuracy.

Conserving Bandwidth & Delivering High Performance
Of any font technology, TrueDoc is the most efficient at storing font data. The font data in a PFR is a fraction of the size of the original font. Along with character subsetting (storing only the characters a document needs, not the entire character set), this ensures that the amount of transmitted or ROM-stored font data is as small as possible.

In addition, TrueDoc PFRs are ready to image immediately. You don't need to decompress the font data first, and you can access the characters randomly at any time. Furthermore, you can download PFRs from servers whenever you need to access them and dynamically merge them with current character subsets. This is particularly important for languages such as Kanji, Korean, and Chinese, whose fonts can contain upwards of 10,000 characters in them--even more when the fonts include "Gaiji" (special) characters.

TrueDoc is also among the fastest pure character generators available in the industry. The TrueDoc CSP can generate characters faster than the native font subsystems of popular operating systems, such as Microsoft Windows and the Macintosh.

Minimizing Embedded Resources
TrueDoc is especially frugal with precious set-top box resources. The basic TrueDoc CSP requires approximately 60 to 80KB of code, depending on the options a developer users. It requires no other rasterizers or decompression routines. A core set of embedded characters will typically take up less than 10KB of data for Latin fonts, under 100KB for Asian fonts.

The total size of the TrueDoc code, as implemented for one customer, is only 78KB. The size of the TrueDoc portable font resources are only 8KB for characters from a Swiss font, 11KB for Dutch, and 12KB for Courier. The small TrueDoc code and the highly compressed fonts allow for the best possible use of memory and the fastest possible character generation.

TrueDoc and the Internet
If a developer implements TrueDoc in the operating system of the set-top box, customers can use the STB with a growing number of Java and web applications to view richly formatted text. Because it can render font data, in the form of TrueDoc PFRs, a TrueDoc-based STB/ITV device will already be Internet ready.

Figure 5. Screen shot of a sample of international characters recorded for a TrueDoc PFR and regenerated on screen in an Internet browser. The zoomed-in box illustrates TrueDoc's anti-aliasing capabilities. (Note the gray pixels at the edges of the character.)

Multilingual Capabilities
TrueDoc can record and render any character shape, regardless of complexity. It is fully compatible with double-byte non-Latin fonts, and it supports languages written vertically or right to left. Because the CSP can render PFR data either stored in the STB's operating system or downloaded from other sources, the interactive TV system can support multiple languages without embedding large amounts of font data in the set-top box.

How Bitstream Meets Market Needs
For software companies who develop operating systems for set-top box manufacturers, Bitstream provides the most advanced and comprehensive font subsystem available, with a business model that fits well with the needs of these developers. The TrueDoc SDK includes:

• TrueDoc Character Shape Player (CSP)
• Core set of PFR fonts, which the CSP can render

Ultimately, the CSP and core set of PFR fonts give operating system developers and set-top box manufacturers two important components for rendering text on the screen:

• High-quality outline characters, from which the CSP can create smooth, well-composed text on the screen, at any size and resolution



• Interactive and multilingual font support, in the form of downloadable PFRs, which the CSP can render on the fly

Conclusion
No other font solution offers the features that Bitstream TrueDoc for ITV does. TrueDoc is becoming widely adopted in the set-top box, digital TV, and embedded systems markets. TrueDoc's small size, high quality, fast performance, and support for all languages (including double-byte languages) has brought TrueDoc to the point where it is becoming the standard for memory-constrained environments. For the ITV market, we have added special enhancements to TrueDoc, which means that developers need look no further than Bitstream for a scalable font subsystem.