Newsgroup: it.comp.hardware.video-3d
Titolo: ATi Filtering Chatlog (lunghetto)

  What follows is the log file of ATi's online chat session with Andy 
Pomianowski, Staff Engineer and Raja Koduri, Engineering manager at ATi 
regarding recent questioning regarding ATi's filtering method on X800 
boards.
TheRock Why are you not doing full AF?
Andy/Raja Would you say that 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.
volt_Bjorn3D I think the whole community appreciates the time and the 
initiative for doing a chat about current filtering algorithm which 
certainly raised a few issues. Question: was the new filtering algorithm 
intentional and if you could tell us why werent review sites notified 
about it. Thanks
Andy/Raja We are constantly tuning our drivers and our hardware. Every 
new generation of hardware provides the driver with more programmability 
for features and modes that were hard-wired in the previous generation. 
We constantly strive to increase performance and quality with every new 
driver release. There are literally dozens and dozens of such 
optimizations that went into our drivers in the last year or so. 
Sometimes many such optimizations are not even communicated internally 
to marketing and PR teams for example. And many optimizations are very 
proprietary in nature and we cannot disclose publicly anyways.
astaroth Is X800's hardware able to do "traditional" trilinear or is the 
new algorithm completely hardwired (not that I would mind ) ??
Andy/Raja The X800 hardware is capable of all features of previous 
generations, and many more besides.
alp Is this bilinear or bri/trillinear as is is supposed to be...i heard 
it is possilby a bug in CoD causing it to set filtering to bi rather 
than a really bad trillinear filtering method, is this true?
Andy/Raja This we believe is test error and the X800 images appear to be 
obtained using only a bilinear filter. We have been unable to reproduce 
this internally. Also, note that the game defaults to bilinear when a 
new card is installed and this may explain the tester error.
Singer Why did ATI say to the general public that they were using 
trilinear by default, when in fact it was something else? (Quality is 
ok, I agree, but you did deceive, by claiming it to be a trilinear)
Andy/Raja We understand that there was confusion due to the recent 
reports otherwise. We provide trilinear filtering in all cases where 
trilinear filtering was asked for. As has been demonstrated many times 
by several people - almost every hardware has a different implementation 
of lod calculation and filtering calculations. If we start calling all 
the existing filtering implementations with different names - we will 
end up with many names for trilinear.
Wer Is bit comparison difference images can highlight IQ differences 
surely there must be some - why do you say there are no IQ differences 
when these comparisons show otherwise?
Andy/Raja The bit comparision differences between implementations occur 
due to many reasons. We constantly make improvements to our hardware 
algorithms. Bit comparisions just say they are different - not 
necessarily that one is better than the other. We always on the lookout 
for cases where we can find IQ problems with our algorithms. We can 
guarantee you that there will be bit-wise mis-matches withour future 
generation hardware too and the future generation hardware will be 
better. Our algorithms are exercized by the stringent MS WHQL tests for 
mipmap filtering and trilinear and we pass all these tests. These tests 
do not look for exact bit matches but have a reasonable tolerance for 
algorthmic and numeric variance.
crushinator Is this Algorythm implemented in hardware? who's analysing 
texture maps, is it just the driver doing that or is it the chip?
Andy/Raja The image analysis is performed by the driver to chose the 
appropriate hardware algorithm. This allows us to continually improve 
the quality and performance with future drivers.
Bouncing Zabaglione Brothers If its so good, why has it remained hidden 
from the public and not marketed as "ATI SmartFilter" or somesuch? 
Surely if its as good as you say (better quality, faster speed), ATI 
marketing should be crowing about it? One of the issue here is that it 
*looks* like ATI is trying to hide things, even if what you have is a 
genuine improvement for the customer.
Andy/Raja The engineering team at ATI is constantly improving our 
drivers by finding ways to take better advantage of the hardware. These 
improvements happen during all the catalyst releases. We might have 
missed an oppurtunity to attach a marketing buzzword to this optimization!
Hanners Can you give a more detailed explanation as to why the use of 
coloured mipmaps shows the use of full trilinear, which doesnt 
correspond to what seems to occur in a normal, real-world situation?
Andy/Raja Coloured mipmaps naturally show full trilinear as our image 
quality analysis reveals that there could be visible differences in the 
image. It should be noted that trilinear was originally invented to 
smooth transitions between mip-levels, and in the original definition 
mip-levels should be filtered versions of each other, as coloured 
mip-levels clearly are not. Despite this, we understand that people 
often make use of hardware for purposes beyond that originally 
envisioned, so we try to make sure that everything always functions 
exactly as expected.
Cthellis From previous comments, there have been mention of this 
technique used for a while (~12 months?) in the RV300 series of chips, 
but most as with R420. can you tell us which cards, which Catalyst 
versions, and/or which games exist where we can see similar tendencies,
Andy/Raja We had new filtering algorithms in places since Cat 3.4 or so. 
Note that the image quality improved over various driver updates since. 
Also, as noted earlier, X800 provides better controls than earlier 
parts. It will be hard to find an exact match with our earlier hardware 
and drivers.
mabru Dont you think such a tradeoff is inconceivable in a 500$ graphic 
card?
Andy/Raja We think that what we do is expected of all our cards, in 
particular the more expensive ones. Our users want the best looking 
results and the highest quality results. They want us to go and scratch 
our heads and come up with new ways to improve things. Users of ATI 
cards from last year want us to come out with new drivers that improve 
their performance and maintain the image quality. We have dedicated 
engineering teams that work hard to improve things. It's an ongoing 
effort, exploring new algorithms, finding new ways to improve the end 
user experience, which is what all this is about. And we are listening 
too; if you don't like what we offer, let us know and we will strive to 
improve things.
anonymouscoward Image quality is a relative term. The real question is, 
"does the claimed 'trilinear filtering' produce a byte-for-byte replica 
of 'true trilinear filtering'?" Whether or not the image quality is "the 
same" or "essentially" the same is irrelevant to this questions
Andy/Raja Byte for byte compared to what? "True trilinear" is an 
approximation of what would be the correct filtering, a blending between 
two versions, one which is too blurry and one too sharp. An improved 
filter is not byte for byte identical to anything other than itself, but 
that doesn't mean it isn't a better approximation.
wild_neo Do you think that you still can compare the benchmarks with 
other brands, even if you use that different approach (non-equivalent 
technique)?
Andy/Raja We've answered this, and yes, we feel we can compare ourselves 
to any brand, as we believe our quality and performance are higher. 
Perhaps at times we should be upset about people comparing us to lower 
quality implementations
Toaster Whats the patent number and filing date of this algo?
Andy/Raja This is in the patent pending process right now. So we will 
not put out the actual patent information at this time. Once approved, 
anyone can go read the patent.
chris What performance boost does this give you, anyway?
Andy/Raja It's a very mild optimization at the default levels, so of the 
order of a few percent. But this is a neat algorithm - we encourage you 
to take the texture slider all the way towards "performance" - we don't 
think you'll be able to see any image change until the very end, and the 
performance increases are significant.
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   What follows is the log file of ATi's online chat session ...
Ho seguito abbastanza da vicino la vicenda dell'anisotropo di ati a suo
tempo e trovo molte analogie anche in questo caso.
Trovo alcune mezze verità in questa chat. Il motivo per cui non hanno
divulgato questi algoritmi è secondo me piuttosto chiaro: una volta spiegato
cosa fanno la concorrenza può farlo uguale (infatti l'as adattivo è oggi in
nv40 in un modo molto simile alla faccia di tutti quelli che a suo tempo
gridarono allo scandalo). E sotto questo punto di vista sono personalmente
d'accordo.
La trovo una implementazione intelligente, come ho trovato intelligente
quella dell'af del tempo.
Non trovo nessuna analogia con quake/quack o con farcry/fartcry, che sono a
mio avviso tutte altre questioni.
Penso anche che la voglia di sensazionalismo di alcuni siti / utenti sia più
legata a sentimenti di rivalsa dettati da un tifo deluso piuttosto che da
basi oggettive. Misurare e confrontare la qualità di un prodotto dalla
quantità di fango sollevato intorno è un approccio che non condivido.
Condivido però chi biasima il marketing di una società per delle aspettative
che ha e che vengono deluse: perciò trovo condivisibile (anche se non sono
d'accordo) chi si aspetta che una cosa come questa debba avere la sua giusta
divulgazione. Per gli stessi motivi, io stesso trovo che le politiche di
nvidia siano la prima causa degli ultimi (da oltre due anni ma solo perchè
prima non c'era una vera alternativa) suoi fallimenti.
Ciao
Milio

 Milio
comunque dicono chiaramente che se l'utenza lo vorrà potra usare il full
trilinear...e questo è l'importante!

 full trilinear...e questo è l'importante!
???
Dicono
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.
Dicono che secondo loro non ce n'è bisogno e pensano di non metterlo ma se
gli utenti lo richiederanno e dimostreranno la sua utilità, potrebbero
considerare l'idea di aggiungerlo
Il che vuol dire tutto fuorchè che si potrà usare un trilinear a scelta..
In poche parole, te lo scordi

 trilinear...e questo è l'importante!
Dicono che se l'utenza lo vorrà valuteranno se impostare una opzione nei
drivers, ma per il momento c'è solo quello.
Credo che non vedremo mai quella opzione, e penso anche che non ce ne sia
alcun bisogno.
Ciao
Milio

 alcun bisogno.
credo che la vedremo ma che non ce ne sarà mai bisogno