Antialiasing image quality - Alpha transparency
Here's one final AA image quality example, focused on the methods that ATI and Nvidia have devised to handle the tough case of textures with alpha transparency cutouts in them. Nvidia calls its method transparency AA and ATI calls its adaptive AA, but they are fundamentally similar. The scene below, again from Half-Life 2, has two examples of alpha-transparent textures: the leaves on the tree and the letters in the sign. 4X multisampling is enabled in all cases. Without provisions for alpha transparency, though, the edges are not antialiased.

Alpha transparency antialiasing quality w/4X AA
GeForce 7900 GTXRadeon X1950 XTXGeForce 8800 GTX
No transparency/Adaptive AA

Transparency multisampling/Adaptive performance mode

Transparency supersampling/Adaptive quality mode

ATI's adaptive performance mode looks to be superior to Nvidia's transparency multisampling mode, but adaptive quality mode and transparency supersampling produce very similar results, likely because both are doing 4X supersampling on the alpha-transparent textures.