Saffron Type System

The Saffron Type System is a system for rendering high-quality scalable type on digital displays. Developed by Mitsubishi Electric Research Laboritories (MERL), Saffron is built on a core of Adaptively Sampled Distance Field (ADF) technology. Saffron has been licensed to Adobe and is shipping in all Flash-based products, including Adobe Flash CS3.

Antialiasing

Saffron performs antialiasing by first computing an ADF and then mapping distance values to densities. This distance-based antialiasing approach renders beautiful curves, captures small details, and preserves the nuances of the original font design. No special mechanisms are needed to avoid dropout. Although only one distance sample is needed per pixel to achieve high-quality results, Saffron can use up to 3 samples per pixel to optimize image quality for LCD displays. The computation of a distance sample requires only linear interpolation and can be updated incrementally from pixel to pixel, thereby making the rendering process simple and efficient.

Math Modes

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.

Glyph Formats

Saffron supports both traditional outline-based fonts and uniform-width stroke-based fonts. 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.

Grid Fitting

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 detects strong horizontal and vertical edges and aligns them to the pixel grid. The MAZ algorithms work with both outline-based fonts and stroke-based fonts, run dynamically during rendering, and operate fully automatically with no user parameters required.

Saffron fully supports application-hinted glyphs. This feature allows applications to override Saffron's automatic grid fitting algorithms by using their own hints (e.g., TrueType hints) to perform grid fitting.

Sub-pixel Rendering

Saffron supports sub-pixel rendering to optimize image quality for LCD displays. Although RGB vertical striped arrays are common, Saffron can also render to alternative pixel patterns such as RGB delta arrays, which are often used on digital camera LCDs. In addition, prototype implementations of Saffron are optimized for Clairvoyante's PenTile patterns. Note that during sub-pixel rendering, Saffron reduces color fringing artifacts that would otherwise be visible and distracting at small sizes.

Continuous Stroke Modulation

Saffron exploits the inherent properties of distance fields to provide Continuous Stroke Modulation (CSM), i.e., continuous modulation of both stroke weight and edge sharpness. CSM allows users to tune the appearance of text to suit their individual tastes. For example, sharper, softer, thinner, and thicker versions of the same typeface can be rendered by using different CSM parameters.

External links

* [http://www.merl.com/people/perry/SaffronWebPage/index.html Saffron website]
* [http://www.merl.com/ Mitsubishi Electric Research Laboritories (MERL) website]
* [http://www.mitsubishi.com/ Portal website for Mitsubishi companies]