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Anisotropic Filtering and FSAA Quality Investigation

But before running theoretical tests, we decided to perform a short investigation of ATI’s new full-scene antialiasing methods to find out whether they are different or not when compared to ATI’s old techniques as well as Nvidia’s coverage sample antialiasing (CSAA).

It is necessary to note that activation of ATI’s new custom-filter antialiasing (CFAA) may seem to be a tricky process for a novice: the end-user needs to select type of filter first and the number of samples second. Given that driver does not explain that “Box” filter is a traditional multi-sample antialiasing (MSAA), whereas “Narrow tent” and “Wide tent” represent the new CFAA, some customers may have to spend additional time finding out a suitable method.

Currently ATI Catalyst driver supports MSAA 2x, 4x and 8x, whereas the “good-old” MSAA 6x, which was introduced back in 2001 along with the Radeon 8500, is not supported in current drivers. In addition, the drivers support CFAA 4x, 6x, 8x, 12x and 16x, whereas the advertised adaptive edge-detect FSAA is not present.

Since CFAA 4x is actually MSAA 2x with “Narrow tent” filter, it makes sense to compare it to MSAA 2x of ATI Radeon and Nvidia GeForce.

CFAA 4x vs. MSAA 2x

Half-Life 2

Radeon HD 2900 XT

Radeon X1950 XTX

GeForce 8800 GTX

CFAA 4x

MSAA 2x

MSAA 2x

Elder Scrolls: Oblivion

Radeon HD 2900 XT

Radeon X1950 XTX

GeForce 8800 GTX

CFAA 4x

MSAA 2x

MSAA 2x

When we first tested Nvidia GeForce 8800 graphics card several months ago, we noticed that the launch ForceWare driver had issues with fog in Half-Life 2. Well, today we have an unpleasant surprise: the new ATI Catalyst driver has the same issue.

It is indisputable that CFAA 4x antialiases lines much better than MSAA 2x. However, we have to admit that it blurs the whole image pretty significantly too, hence, this may not be a really good solution for games that have sharp textures.

All of our today’s participants support MSAA 4x, so we can compare realization of multi-sampling on all GPUs.

MSAA 4x vs. MSAA 4x

Half-Life 2

Radeon HD 2900 XT

Radeon X1950 XTX

GeForce 8800 GTX

MSAA 4x

MSAA 4x

MSAA 4x

Elder Scrolls: Oblivion

Radeon HD 2900 XT

Radeon X1950 XTX

GeForce 8800 GTX

MSAA 4x

MSAA 4x

MSAA 4x

It is interesting to note that the new Radeon HD 2900 XT renders sharper image compared to the Radeon X1950 XTX and GeForce 8800 GTX. It is hard to tell, however, whether the new R600 produces better antialiasing quality compared to the G80, as on some lines MSAA filter of the GeForce provides smoother quality, whereas in other cases MSAA filter of the Radeon leaves its rival behind.

6x CFAA mode has two types of realization in the current driver: as MSAA 2x with “Wide tent” filter and as MSAA 4x with “Narrow tent” filter. We decided to compare these two methods to MSAA 4x of the Radeon HD 2900 as well as with MSAA 6x of the Radeon X1950 XTX.

CFAA 6x vs. MSAA 6x

Half-Life 2

Radeon HD 2900 XT

Radeon HD 2900 XT

Radeon X1950 XTX

CFAA 6x w. Narrow tent

CFAA 6x w. Wide tent

MSAA 6x

Elder Scrolls: Oblivion

Radeon HD 2900 XT

Radeon HD 2900 XT

Radeon X1950 XTX

CFAA 6x w. Narrow tent

CFAA 6x w. Wide tent

MSAA 6x

Unfortunately, 6x CFAA with “Wide tent” filter leaves aliasing artifacts on the image in addition to blurring textures, which is logical, as the number of colour samples remain the same as in the case of 2x MSAA, whereas the amount of blurring the driver has to apply on the image become gargantuan.

6x CFAA with “Narrow tent” filter looks indisputably better compared to its incarnation with “Wide tent” filter and two colour samples, as the mode is an improved version of usual MSAA 4x. In fact, the 6x CFAA with “Narrow tent” filter can even be compared against 6x MSAA: perhaps, it antialiases even better. Unfortunately, sampling from outside pixel’s boundaries has its negative effect: the whole image a little blurry.

As we know from our GeForce 8800 GTX review, CSAA 8x is not as good as FSAA 8xQ, which is basically MSAA 8x, still, it is not easy to notice any difference without special tools. But let’s take a look at ATI’s MSAA 8x implementation with the Radeon HD 2900 XT hardware.

CFAA 8x vs. MSAA 8x vs. CSAA 8x vs. CSAA 8xQ

Half-Life 2

Radeon HD 2900 XT

GeForce 8800 GTX

CFAA 8x

CSAA 8x

MSAA 8x

CSAA 8xQ

Elder Scrolls: Oblivion

Radeon HD 2900 XT

GeForce 8800 GTX

CFAA 8x

CSAA 8x

MSAA 8x

CSAA 8xQ

MSAA 8x of the Radeon HD 2900 XT is a little better compared to FSAA 8xQ of Nvidia GeForce 8800 in case of Elder Scroll: Oblivion title. Unfortunately, we cannot verify this for the case of Half-Life 2 due to the fact that R600 has issue with fog rendering with this game title.

Even though 8x CFAA with “Wide tent” filter looks normal and provide high-qaulity antialiasing, it also blurs textures and small details do not look really crispy with this MSAA 4x antialiasing with special filter applied.

Formally, the remaining CFAA 12x and CFAA 16x are competing against Nvidia’s FSAA 16x. Well, let’s see the difference.

CFAA 12x vs. CFAA 16x vs. CSAA 16x vs. CSAA 16xQ

Half-Life 2

Radeon HD 2900 XT

GeForce 8800 GTX

CFAA 12x

CSAA 16x

CFAA 16x

CSAA 16xQ

Elder Scrolls: Oblivion

Radeon HD 2900 XT

GeForce 8800 GTX

CFAA 12x

CSAA 16x

CFAA 16x

CSAA 16xQ

It is undeniable that both CFAA 12x (MSAA 8x with “Narrow tent” filter) and CFAA 16x (MSAA 8x with “Wide tent” filter) provide acceptable quality of antialiasing. Nevertheless, blurring becomes too significant in case of CFAA 16x and can also be noticed in case of 12x. A good thing about ATI’s CFAA is that vegetation looks a little more accurate, but small texture details may nearly disappear due to blurring. Therefore, we have to say that Nvidia’s FSAA 16x and FSAA 16xQ look much better than competing modes from ATI. Still, we yet have to see ATI’s adaptive edge detect filters.

So, lets sum everything up:

  • CFAA 4x is better than typical MSAA 2x, but it blurs image.
  • CFAA 6x with “Wide tent” filter blurs image too heavily and the quality of this antialiasing is worse than typical MSAA 4x.
  • CFAA 6x with “Narrow tent” filter provides antialiasing quality that is on par with MSAA 6x. Nevertheless, it also blurs image.
  • CFAA 8x with “Wide tent” filter looks ok, but it still blurs image quite significantly.
  • CFAA 12x with “Narrow tent” filter is better than typical MSAA 8x, but the blur is present as well.
  • CFAA 16x with “Wide tent” filter blurs textures too heavily.

Now, let’s have a look at anisotropic filtering quality.

Anisotropic Filtering

Radeon HD 2900 XT

Radeon X1950 XTX

GeForce 8800 GTX

Default Quality

High Quality

High Quality

Without any surprises, ATI Radeon HD 2900 XT has the same good adaptive anisotropic filtering algorithm that we know from the introduction of ATI Radeon X1000. Nonetheless, current generation of Nvidia GeForce 8800 graphics cards provides even better angle-independent anisotropic filtering and it is not completely clear why ATI decided not to improve this part of its new chip.

 
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