DXT issue NOT fixed in GF4 Series ?

[Guest]

From the DirectX Developers Mailing List :

FWIW, the DXT issue hasn't been fixed on GF4 cards - the card now simply dithers in texture space which looks better in some cases but worse in others.

-- Daniel, Epic Games Inc.

So after all these years and chip releases they still can't do a simple interpolation with 24/32 bits rather than 16 bits ? Has anyone seen these issues that Daniel refers to ?

Dissapointing... and

G~

 

[easyride]

Oh boy... guess I won't be buying a GF4 after all!

 

[Nappe1]

Oh boy... guess I won't be buying a GF4 after all!

don't jump on the gun yet.

I would too hear about this problem... is this really true?

 

[Humus]

Is there any way for us to see that it "dithers in texture space". Screenshot? Test app?
It sounds really odd to try to patch it like that instead of just adding a few bits of interpolation.

 

[Kristof]

Rev, you talk to daniel at EPIC, not ? Maybe you can ask him about this ?

 

[OpenGL guy]

Is there any way for us to see that it "dithers in texture space". Screenshot? Test app?
It sounds really odd to try to patch it like that instead of just adding a few bits of interpolation.

What makes you think they'd simply have to add some bits of interpolation? It sounds like they are decompressing the texture into the texture cache, so they want to save space by only using 16-bits per texel when possible. The old hack they used was to promote the textures to DXT5 where they most likely used 32 bits per texel in the cache. Of course, this can impact performance.

I sincerely doubt it's a matter of interpolation...

 

[crypto1300]

The S3TC quality in Jedi Knight II & Q3 is pretty bad with my GF4 Ti4400. When S3TC is turned off it looks much better, but is unbearably slow. Enabling 3TC quality trick in RivaTuner does help alot & keeps the speed increase that S3TC offers, but the quality is not quite as good as turning off S3TC completely.

 

[Sharkfood]

Hmm.. I don't know if Jedi Knight II is a good example of how TC should look as it looks horrible on just about any card (not just NVIDIA cards) with TC on.

This is on a Radeon 8500 showing TC off and on side by side:
http://shark_food.tripod.com/jk2/tc.html

 

[Geeforcer]

Humm, that does look crappy... What did Raven do?

 

[OpenGL guy]

Humm, that does look crappy... What did Raven do?

Looks like they chose poor textures for compression. DXTC looks best on textures where there aren't large changes in color values between adjacent texels. If you need to have large changes in color values, then you will probably be ok if the changes occur on 4x4 block boundaries. Another problem is that DXTC doesn't handle areas with high contrast well at all.

Check out the lightmaps in Quake 3 for a good example of when NOT to compress textures... just be _absolutely sure_ that the card you are looking at is really compressing the lightmaps to begin with.

 

[Doomtrooper]

Since Shark was nice enough to upload some 8500 shots where is the screen shots of the Geforce 4 cards that this thread is about, Reverend has that ability as does Dave Baumann along with probably 60% of this boards members..Matt Burris...someone show some pics..it would be only fair to see what the original poster was talking about

 

[Prime]

If there aren't any by the time I get home this evening, I'll post some from my GF4 4400. I have no idea what it looks like, so it will be interesting to see. I just don't see the need for it on a fast 128MB card.

Edit: Shark, where exactly is that in the game? SP maps or MP maps? Or can I get that floor texture anywhere?

 

[Prime]

Well, here they are, but I really don't see much difference in them...I think maybe the area I'm at isn't a good example of TC?

http://www.jdwarner.com/screens/screens.htm

 

[easyride]

I just don't see the need for it on a fast 128MB card.

A 128 MB, high bandwith card may not need TC for current games, but what about, say, UT2003 with 1024*1024 textures?

 

[Prime]

A 128 MB, high bandwith card may not need TC for current games, but what about, say, UT2003 with 1024*1024 textures?

I'll either turn it on or buy a faster card. At this point, nothing I play needs it, so I don't use it.

 

[Prime]

I updated the page with some Q3 sky shots as well. The quality is definitely better than the GF3 rendering, but it still is somewhat lacking.

http://www.jdwarner.com/screens/screens.htm

 

[Dave B(TotalVR)]

Well pardon me for suggesting VQ texture compression should replace S3TC 8)

 

[easyride]

Yup, either that or FXT1 8)

 

[andypski]

Dave B-

I don't suppose you could compress this texture using VQ to show us how good it looks.

I would be very interested to see the results at equivalent bit depth (4-bit) or alternatively at higher compression ratios.

I doubt FXT1 would appear any better than DXT1 on the sky because:

1. The endpoint resolution is lower (555 vs. 565), so any problems with effective bit-depth could actually be increased.
2. The block size is twice as large at 4x8 vs. 4x4, and the color mapping problem is more difficult for the compressor because one of the interpolants is now shared between adjacent 4x4 areas. Blocking artifacts would probably therefore be aggravated, introducing more noticeable low-frequency noise.
3. The alternative FXT block formulations are not designed to help with this sort of case as I recall, and probably would be of limited use.

Cheers
- Andy.

 

[Basic]

While FXT1 uses some nice tricks, do remember that FXT1 uses 15 bit color where DXTC uses 16 bit. It is possible to modify FXT1 so that you get 16 bit on at least some colors though.

It should also be noted that someone would have to write a new FXT1 compressor. The one 3dfx had done was horribly slow, on the verge of uselessness. They even pledged for fans to write a faster one...