[ft] Gamma (?) huge difference between FreeType and others (OS X, or even FreeType based MacType)

[puxi]

I'm fully confused. I don't know how to say properly, because I'm not
talking about font's darken/slightly, I'm saying, they just like got
the different "colors" of the results.
Here are some sreenshots (I use Firefox to compare them),
OS X
https://i.imgur.com/XEO7HY0.png
https://i.imgur.com/fQlKntl.png
https://i.imgur.com/xtVscsr.png

Linux/FreeType2 2.5.5-1
https://i.imgur.com/xoOJ4HN.png
https://i.imgur.com/7WJULvj.png
https://i.imgur.com/IOqdU9i.png

MacType (MacType is FreeType based, more details see bottom external links)
https://i.imgur.com/z5vuZQe.png

!!Especially when setting font's gamma valve to high level as that
makes font get more slightly.
MacType with font gamma changes
https://i.imgur.com/n7yhlXj.png

Linux/FreeType with font gamma changes (I use INFINALITY patch to
tweak the gamma value)
https://i.imgur.com/PsGXzmB.png
https://i.imgur.com/9z77xnb.png

Putting them together,
https://i.imgur.com/dpDEEzO.png
https://i.imgur.com/EJdaCQQ.png

As you can see, even the MacType got the results as same as OS X. Only
Linux is so different.  Still not sure it is a "Gamma correction"
issue. If not, what is making Linux font rendering so "weird"?
How to fix it?
Thanks!

External links:
History of gdi++
http://a.pomf.se/vlgkcm.txt