New from Typekit: Improved font rendering on Windows
July 26, 2011
As part of our ongoing work to improve type rendering, we’re rolling out some changes to the font outlines we deliver. To explain how this works, let’s first review how font files are rendered, and then look at some examples to show how we can improve upon them.
In previous posts, we’ve discussed how font files typically include outlines in one of two formats: TrueType or PostScript. TrueType outlines can include detailed instructions (usually referred to as “hints”) which provide additional information to the rendering engine. Hints can resolve the warts and inconsistent stroke widths that plague fonts in Windows browsers.
At small sizes (and especially when a font has been well-hinted), the Windows GDI rendering engine, with ClearType enabled, makes for clear, crisp rendering. But GDI’s ClearType subpixel antialiasing only works in one direction (horizontally). GDI ClearType does not smooth letterforms vertically, so diagonal strokes and curved strokes — especially at large sizes – can look pixellated, even if a font is well hinted.
DirectWrite — the default rendering engine in IE9, and enabled via a user preference in Firefox 4 — corrects this problem; it uses ClearType subpixel antialiasing for horizontal smoothing, and also smooths letterforms vertically. However, many users have yet to upgrade and are stuck with GDI ClearType. And unfortunately, no amount of hinting can correct this.
There is a solution, however: due to a quirk in the GDI rendering engine, PostScript outlines cannot be rendered with ClearType, but rather display using grayscale antialiasing. Grayscale antialiasing smooths in both directions, and looks great at large sizes. So we can improve this rendering scenario by serving PostScript outlines instead of TrueType.
Starting today, we’re serving PostScript outlines for a number of fonts: Underware’s Bello Pro, as well as Calluna, Lapture Display, and Quatro. In each case, the rendering of the font is significantly improved:
If you’re using these fonts, republish your kits to get the updates. We’re working closely with our foundry partners to identify additional fonts in the library that would also benefit from PostScript serving, and we’ll be rolling those out as we can. Stay tuned!