Chat Transcript: ATI's texture filtering algorithms

Date: Wednesday May 19, 2004
Time: 3:00PM - 4:30PM EST

Below is the transcript from today's chat session on ATI's trilinear filtering. We're posting it here to give as many people as possible the opportunity to see the answers to the questions. Because the technical issues slowed down our ability to answer your questions, we added another hour to the session, and I believe we covered the major points. However, we apologize for the technical difficulties - we wanted to respond as quickly as possible to address people's concerns, and appear to have got ahead of the technology.

Moderator
Thanks for joining us this afternoon. With me are Andy Pomianowski and Raja Koduri, two of the main people behind our performance and image quality algorithms. The chat will last for one hour. We will attempt to answer every question. If you don't see an answer to your question immediately, please be patient, because it can take five to ten minutes for our answers to be posted on the website. Start submitting questions!

TheRock
Why are you not doing full AF?

Andy/Raja
Our AF is not "full" AF? After all, we've been using an adaptive method for this since the R200. If you select 16x in the control panel, you may get 8x, 4x, or 2x depending on how steeply angled the surface is. Doing 16x AF on a wall you're viewing straight on would look exactly the same as no AF, but require 16x more texture samples. Why would it make any sense to do this? This is exactly the same idea we're using for trilinear filtering.

Rush
Why are your trilinear optimizations different to what Nvidia is doing?

Andy/Raja
We won't comment on competitor's algorithms. Our focus is to retain full image quality while offering the best performance possible.

No-one is suggesting that our texture filtering algorithms produce a worse output than previous generations. In fact, if we took them out now the speed would be marginally less and we will receive complaints from users that our quality is lower. We did receive feedback from several folks who think that the X800 IQ is better than our 9800 series - it is always our goal to improve quality in newer hardware generations. To assist in this we have many additional quality controls in hardware in X800 series than on 9800.

Our target is also to avoid any need to detect applications, and as such we have to try to be sure that our image quality remains high in all cases. To achieve this we spent a lot of effort developing algorithms to make the best use of our quality tuning options. This isn’t a performance enhancement applied to popular gaming benchmarks; it’s a performance boost – without image degradation – applied generically to every game that uses box-filtered mipmaps, which is most of them. This means, incidentally, that it’s working during the WHQL tests (unlike optimizations activated by application detection), which means that it has to meet the very stringent image quality requirements of those tests.

TheRock
Will full trilinear filtering be allowed to be set in the drivers?

Andy/Raja
We try to keep the control panel as simple as possible (even as its complexity increases), and if the image quality is identical or better there doesn't seem to be a need to turn it off. However, if our users request otherwise and can demonstrate that it's worthwhile, we would consider adding an option to the control panel.

Singer
Is this really trilinear filtering?

Andy/Raja
Yes, It's a linear function between the two mipmap levels based on the LOD.

gs.
When will ATI restore full trilinear so that review sites can actually rebench and retest your cards, since any previous review benchmarks is invalidated by this cheat/optimisation/whatever?

Andy/Raja
We have never removed "full trilinear". We certainly do not believe that any benchmarks have been invalidated by our techniques. In all cases reviewed so far we believe that we have higher image quality than other implementations.

Sphinx
Is Ati cheating if Colored MipMaps are enabled and shows True FULL_TRI AF and Only Then. Like the Article in ComputerBase.de Descripe it as such one.

Andy/Raja
Absolutely not. If it were the case that we were only performing full trilinear with coloured mipmaps then you might have a point, but this is emphatically not what we do. We take advantage of properties of texture maps for performance and IQ gains. In cases where we are not able to determine that the texture content is appropriate for these techniques we use legacy trilinear filtering. This includes cases such as dynamically uploaded texture maps where we avoid performing analysis so as not to cause any possible gameplay hitches.

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