NVIDIA GeForce GTX480 Video Card Review :: Anti-aliasing

03-26-2010 · Category: Hardware - Video Cards

By Benjamin Sun

The GF100 has six ROP partitions with eight ROP units on each ROP partition. This is a twofold increase over the GT200 which had four ROP units per partition. Each ROP unit can output a 32-bit integer pixel per clock, an FP16 pixel over two clocks or an FP32 pixel over four clocks. Atomic instruction performance is also faster by up to 20 times than the GT200 architecture.

Ok so what does this mean in real-time? The GF100 is expected to offer high performance with 8X MSAA, as the chip has more than three times the texture sample units of the GT200 and is geared to performance with 8X MSAA in mind. By way of comparison, the GeForce GT200 chip was architecture with 4x MSAA in mind, as it is limited in performance when 8x is enabled (8XQ).

The GF100 has a new mode for anti-aliasing, 32X CSAA. Coverage Sample anti-aliasing takes the color values of the FSAA such as 4x or 8x and applies coverage samples to the pixel to smooth out lines without paying the color sample cost of storage. In 32x CSAA the color values of 8x MSAA is stored with 24 additional coverage samples taken to give better image quality than 8x by itself. The GF100 supports alpha to coverage testing which can allow the GF100 to blend fences, foliage and other fake geometry that many games use. The GF100 can take up to 32 samples per pixel allowing up to 33 levels of transparency, compared to the 8 levels on the GT200.

Transparency Anti-aliasing was introduced on the GeForce 7800GTX (G70) to fix issues with alpha to coverage on DirectX 9 games. The G70 was a DirectX 9 card and games that use TMAA that the G70 supported can look better with TMAA on. For the most part, TMAA is not a valid option as it doesn’t really fix billboard aliasing. With the GF100 and alpha to coverage, TMAA will have higher image quality in games that use it. The majority of games released today are still DirectX 9 based with Left 4 Dead 2 being an example, and TMAA will improve the image as it turns on alpha to coverage on DX 9 games.