Re: [ft-devel] State of autohinter stem darkening

[Dave Arnold]

On 10/22/2015 12:55 PM, Nikolaus Waxweiler wrote:
>  Mac OS X is probably doing it that way (Dave? ;)).
I haven't checked lately, but a couple of years ago, Apple (MacOS and iOS) was 
doing something strange.

There were indeed using linear blending for subpixel/LCD rendering. Here, there 
is an additional requirement. You need to blend in a linear color space in 
order to cancel out the color fringing. They used gamma 2.0.

But Apple was using non-linear blending (gamma 1.0) for grayscale antialias. I 
don't know why, unless it was some kind of compatibility goal with older 
versions of the OS. This caused really strange effects when the rendering mode 
changed, as it did for an iPad rotated from landscape to portrait. There were 
even bloggers suggesting that you needed to switch to a lighter weight font in 
portrait mode, without understanding why. They just noticed that the black text 
looked heavier when linear blending was turned off.

Microsoft Windows has been doing linear blending for a long time (20 years?) for both 
grayscale and "ClearType". They used a default gamma of 1.4, but starting in 
Windows XP gave users the ability to configure gamma.

I believe Google's Android has a default blending gamma of 1.4, but individual 
vendors are free to change this, and some do.

-Dave