Ati Catalyst 9.11 delivers higher visual quality to Radeon HD 5000 series
AMD's Radeon HD 5000 graphics cards offer high quality Supersampling Anti Aliasing. The new Catalyst 9.11 delivers a small adjustment that increases the quality even further. PC Games Hardware checks the difference.
In our review of the Radeon HD 5870 we already mentioned it: Ati's new graphics cards are able to run Sparse Grid Supersampling Anti Aliasing (SGSSAA). This feature is interesting because it deals, in contrast to conventional Multisampling Anti Aliasing (AA), with the whole picture and thus also smoothes textures and pixel shaders. With the Catalyst 9.11 WHQL or the Hemlock Beta driver the SSAA get even better.
When Supersampling is applied to a scene this means that all pixels are scanned/worked on more often than required by the rules of the renderer. This oversampling costs, depending on the SSAA level, between twice and eight times as much performance than the calculation of the original scene without SSAA. If a game does not flicker, no additional sampling is necessary since the image only gets a minimal benefit. But in some cases oversampling also results, from a subjective point of view, in a less sharp picture because high frequency details are filtered. In order to draw an advantage from Supersampling in such a case one has to adjust the LOD. This makes sure the right texture resolution is used in the right time. If the driver does not change to low resolution textures in time, the part of the image that is far away can flicker, while the picture gets washy when the high-res textures are not used in time.
If the Texture LOD is adjusted without applied SSAA, this means set to a negative value, this also causes (extreme) flickering. Only Supersampling can eliminate that and results in sharp but still untroubled textures.
SGSSAA: Now with adjusted Texture LOD
After this small theoretical discourse we get to the actual topic. Up to now the Ati driver was able to activate Supersampling Anti-Aliasing but the Texture LOD remained on the default value (0). But with 2x SSAA a value of -0.5, with 4x SSAA -1 and with 8x SSAA even -1.5 would have been better. In other words: A game with 4x SSAA/LOD -1 and 16:1 Anisotropic Filtering is effectively displayed with 32:1 AF. Without an LOD adjustment there is no additional AF. Up to now LOD adjustements were possible in the Windows registry or with the Ati Tray Tools - and one could set full numbers only, which means that an optimal settings was possible for 4x SSAA only.
With the new Catalyst the problem is history. The driver "secretly” adjusts the LOD - just as it should be actually. The result is a sharp picture delivered without an extra tool or additional performance costs. Below you can see a comparison from Crysis Warhead.
Fallout 3 + HD Texture Pack:
But what LOD is used for which SSAA level? Our test reveals that the driver doesn't go to the theoretical limit. It seems like for 4x SSAA a LOD value between -0.5 and -1.0 is used, although -1.0 actually would be correct. See the example below:
The driver uses an LLOD value slightly higher than -1.0 but smaller then -0.5. We weren't able to find out why this is the case, yet, and up to now AMD did not answer our question. We assume that Ati wanted to implement an intelligent solution. Intelligent means that a correct LOD plus Supersampling would again cause flickering objects since due to the LOD high frequent content is sharpened, too. By cutting about 0.2 texture sharpness you get quite a good compromise: Sharp, but no flickering - sharper than without LOD adjustment.
Conclusion: The LOD adjustment of the driver features makes sense and fans of the quality modes will appreciate it for sure. The texture quality is increased without a performance disadvantage or flickering.
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