Fractional Advance Widths vs. Advance Phantom Point


Hello Typophiles,

Apologies for the nerdiness on a first post.

In the midst of some last checks before releasing my first real font, I noticed an unpleasant beating frequency effect on repeated characters at smallish ppems when testing on Windows 7 with the "Natural" mode of DirectWrite ClearType rendering (tested via Firefox with the Anti-aliasing Tuner add-on). The characters phase in and out of different degrees of bluriness.

With a bit of investigation, it looks like this is due to fractional advance widths. I was hoping to be able to control for this by slightly adjusting the advance width phantom point via TrueType hinting. However, it looks like Windows is ignoring that in this rendering mode and using only the designed width instead.

@font-face rendering


I made this just as a general info for those uniformed.

It is simplified, but generally speaking these are main possible paths with default settings.

X axis is market share (with some guessing).

I know a small examples of renderings could be included for better understanding, and I will post this & other refinements later.

A few things not mentioned:
Linux with FreeType rendering, but I have no idea how many people use subpixel rendering or other settings. Each setting has probably less than 1% of users.
Quartz rendering does also other types than subpixel AA, but I would say they are in minority (I really don't know).
There is also an old version of Safari, with Quartz rendering on Windows with default setting.