The Saffron library offers both floating-point and fixed-point implementations of the renderer with identical image quality. The fixed-point implementation is ideal for embedded systems and mobile devices, which often lack floating-point hardware. Porting Saffron from an Intel desktop machine to a Windows Mobile 5.0 device (see above) required only a simple recompile.

Saffron supports both traditional outline-based fonts (left) and uniform-width stroke-based fonts (right). Stroke-based fonts are useful for memory-constrained applications (e.g., embedded systems) because they occupy a much smaller footprint than outline-based fonts and are also faster to render. For example, outline-based fonts containing the GB2312 character set often require well over 3 MB of storage, whereas the same character set can be represented compactly in a stroke-based font with only 250 KB.

Saffron features an automatic grid fitting system that aligns strong vertical and horizontal edges of glyphs to the pixel grid or to the sub-pixel grid. This grid fitting system provides better contrast, uniform stroke weights, and consistent characteristic distances. Standard Alignment Zones (SAZ) currently support several alphabets, including Arabic, Devanagari, Hebrew, Latin, and Thai.

The SAZ grid fitting system requires no changes to existing typefaces and is particularly advantageous when hints are unavailable or have been removed to save space. Unhinted fonts typically occupy significantly less space than their hinted counterparts.

Saffron also features an automatic Multiple Alignment Zone (MAZ) grid fitting system, which is optimized specifically for Asian character sets such as Chinese, Japanese, and Korean. MAZ grid fitting leads to dramatic improvements in rendering quality.

The MAZ grid fitting system requires no changes to existing typefaces and is particularly advantageous when hints are unavailable or have been removed to save space. Unhinted fonts typically occupy significantly less space than their hinted counterparts. Furthermore, manually hinting a typeface is labor-intensive and expensive, especially for Asian character sets.

The Multiple Alignment Zones (MAZ) grid fitting system detects strong horizontal and vertical edges and aligns them to the pixel grid. The MAZ algorithms are optimized for Asian character sets, work with both outline-based fonts and stroke-based fonts, run dynamically during rendering, and operate fully automatically with no user parameters required. This powerful combination of features makes it easy to integrate MAZ into existing applications — just turn on MAZ and watch the rendered glyphs improve dramatically in quality.

Chinese, Japanese, and Korean characters often contain many strokes which are difficult to render distinctly at small sizes (left column). Simply aligning horizontal and vertical strokes to the pixel grid (e.g., by rounding each stroke to the nearest grid point) is not sufficient to produce a clear image and can often lead to disastrous results (middle column). Saffron's fully automatic Multiple Alignment Zone (MAZ) grid fitting system performs character simplification (as needed) to ensure that each character remains clear and legible, even at small sizes (right column). Actual-size renderings at 14 pixels/em are shown to the bottom-right of each diagram.

Saffron's character simplification works for both outline-based fonts and stroke-based fonts.

During sub-pixel rendering, Saffron reduces color fringing artifacts that would otherwise be visible and distracting at small sizes (see bottom row).

Click here to see additional examples of text rendered by Saffron with color reduction enabled.

Outline-based Asian fonts often require 5 to 10 MB of storage, which is problematic for memory-constrained devices such as cell phones. In contrast, uniform-width stroke-based fonts (USFs) require significantly less storage — for example, the GB2312 character set can be represented compactly with only 250 KB. However, since each stroke has a uniform width (top-left image), USFs lack the expressiveness and the cultural acceptance of their outline-based counterparts. We are currently developing an improved representation for stroke-based fonts called Stylized Stroke Fonts (SSFs) which will provide the best of both worlds: the expressiveness of traditional outline-based fonts and the small memory footprint of USFs. A primary goal of this research project is to develop algorithms that can automatically convert outline-based fonts to SSFs.

SSFs can also save memory by representing multiple fonts using a single set of stroke skeletons, as illustrated above. The top-left image shows a USF; the other three images were produced by our prototype SSF renderer and demonstrate the ability to create interesting and different stylistic renderings from the same stroke skeletons. These additional font styles require minimal storage overhead.

In a continuing effort to make Saffron even easier to use, we are currently investigating fully automatic methods for determining high-quality CSM values for a given typeface. This can be done by applying our Multiple Alignment Zones (MAZ) algorithms to analyze characteristic distances (see two examples above). This research will enable applications to determine good CSM values, even with previously unencountered typefaces.