How gamma distortions affect color fringing

Piotr Grochowski

When the ClearType tuner gives you this choice:


This is what you're really choosing between:


If you simply disable ClearType, the renderer is classic GDI, this is what it renders.


and of course text in classic GDI is anti-aliased vertically too, because ClearType GDI has a (probably intentional) glitch in most versions of Microsoft Windows that have ClearType where it would disable vertical anti-aliasing regardless of the gasp setting.

Piotr Grochowski

In ClearType Gray, the gamma distortions look like this:

(except for the bottom right one, which is approximately undistorted)

Arguably, this is even worse because the gamma distortions are no longer distributed between the three channels, causing uneven stem weights (the slightly sloped lines ARE of the uniform weight). We need to raise awareness for this issue because most DirectWrite flavors use a gamma distortion, and most renderers using FreeType misuse its anti-aliasing and therefore use a gamma distortion as well.