View Full Version : IXBT's article on trilinear
Anything that makes news is good for reviewers and their websites in their eyes.
are you suggesting that they're complaining just to make news?
they couldn't have possibly been a little upset that they thought they were testing full trilinear and in fact they weren't, ... could they?
Lfctony
05-24-04, 06:47 PM
Yes, its the reviewers' fault. Whatever makes you sleep at night buddy. :lame:
are you suggesting that they're complaining just to make news?
they couldn't have possibly been a little upset that they thought they were testing full trilinear and in fact they weren't, ... could they?
Does anyone get upset that the graphics companies don't use proper square root and sine/cosine implementations in their asic maths? Instead using approximations and lookup tables? No didn't think so. They still call it sin() and treat it as such as long as it's withing the limits of tolerable error. It's clear that Ati's approximation is extremely close to the "full" implementation. As an engineer I'm impressed.
Does anyone get upset that when windows draws a circle it cheats by using Bresenham's Circle Algorithm, and never actually uses PI or sine...? It's still 99.9% circle, and saves a massive ammount of work.
Does anyone get upset that the graphics companies don't use proper square root and sine/cosine implementations in their asic maths? Instead using approximations and lookup tables? No didn't think so. They still call it sin() and treat it as such as long as it's withing the limits of tolerable error. It's clear that Ati's approximation is extremely close to the "full" implementation. As an engineer I'm impressed.
Does anyone get upset that when windows draws a circle it cheats by using Bresenham's Circle Algorithm, and never actually uses PI or sine...? It's still 99.9% circle, and saves a massive ammount of work.
wow I didn't know they were doing that! I'm upset!
and as a 3d artist! I'm not impressed!
And as a consumer, I say...
"Burrrrp!" :D
Taz
Couldn't reviewers simply compare screenshots / actual gameplay / slowmotion video captures / electron microscopy then decide that x is worse than y?
Or does the reviewer first need to know that x uses a different algorithm before they can proclaim that it is indeed worse than y? :bash: If this algorithm is indeed so evil, we would all have noticed it a long time ago.
This is how it happened with Nvidia's Brilinear (3dcenter.de exposition attempting to find source of performance gain in ut2003 with new drivers), it looks like how it is happening with ATI's as well.
trashcan
05-25-04, 12:58 AM
Where the hell do people get off with saying the ATI has better graphics then Nvidia. I have both a ATI 9600 and a Nvidia 5700 and my own eyes tell me not only is the 5700 a faster card but also has a brighter and better picture then the ATI card. For the most part both cards look good,and perform good. You cant go wrong with either card ,im sick of listening to ATI fans say how much better ATI is and how much junk the FX line of cards was. That is a lie.
Sorry had to vent listining to all these folks make excuse's for ATI cheat and trolling. This is a NVnews, most folks come here for stuff about nvidia,and not to trash everything nvidia and start trouble.
I don't why people are impressed with ATI's filtering, from those pictures you can see big quality differences, ie the angle dependancy is harsher in ATI's AF, the filtering quality is more ditthered, because of the low quality bilinear filter, ie 5 bit. And the brilinear is very much the same as nvidias and people were'nt very impressed when that was forced onto them. Looks like ATI's filtering is a low quality as they can get away with, not good enough and for a while now i often wondered why i saw dithering in my games that i never noticed before using a radeon card.
Where the hell do people get off with saying the ATI has better graphics then Nvidia. I have both a ATI 9600 and a Nvidia 5700 and my own eyes tell me not only is the 5700 a faster card but also has a brighter and better picture then the ATI card. For the most part both cards look good,and perform good. You cant go wrong with either card ,im sick of listening to ATI fans say how much better ATI is and how much junk the FX line of cards was. That is a lie.
Sorry had to vent listining to all these folks make excuse's for ATI cheat and trolling. This is a NVnews, most folks come here for stuff about nvidia,and not to trash everything nvidia and start trouble.
The 9600 was supposed to match up to the 5600, which it it did quite well. What the 5700 being faster than the 9600 has nothing to do with this thread. People get off saying that ATI cards have better IQ because that's their opinion. Nothing to do with hell or damnation. The FX is junk IMHO, fair enough it does the job it's designed to do, but comparing it to R3x0 or NV40...
The 9600 was supposed to match up to the 5600, which it it did quite well. What the 5700 being faster than the 9600 has nothing to do with this thread. People get off saying that ATI cards have better IQ because that's their opinion. Nothing to do with hell or damnation. The FX is junk IMHO, fair enough it does the job it's designed to do, but comparing it to R3x0 or NV40...
I don't know how you come to that conclusion. Last year when I was shopping for my new vid card. I set a max budget of $200. The FX5700U and 9600XT were both about $180. Hence my descision to go witht he 5700U. If the 9600 is not supposed to compete with the 5700 then why are they the same price?
jbirney
05-25-04, 10:32 AM
"the images received on chips ATI, will sometimes look more precise, and the images received on chips NVIDIA, - more dim, but at movement of the chamber of video, received on chips ATI, will be more inclined to occurrence of moire and "песочка" (dithering), arising because of an insufficient filtration (under-filtering)."
There goes the "IQ is the same" theory.
Does trilinear do anything to help filter out Moire patterns? Have not had a chance to check the article yet...page is loading slow. I can see dithering but Moire as a side effect of lack of full trilinear? Don't buy that one yet.
Does trilinear do anything to help filter out Moire patterns? Have not had a chance to check the article yet...page is loading slow. I can see dithering but Moire as a side effect of lack of full trilinear? Don't buy that one yet.
well, yeah dude, it will dampen the effects of moire patterns, because it's "bluring" textures that are far way on the horizon.
I can post some stills from 3d apps of textures that will prove this in a simular manner that trilinear filtering works.
Lfctony
05-25-04, 02:21 PM
Does trilinear do anything to help filter out Moire patterns? Have not had a chance to check the article yet...page is loading slow. I can see dithering but Moire as a side effect of lack of full trilinear? Don't buy that one yet.
Apparently, it wasn't so noticable with the R3xx cards, so it is something caused by ATI's new filtering method. Seems logical enough.
smeagol
05-25-04, 02:28 PM
are you suggesting that they're complaining just to make news?
they couldn't have possibly been a little upset that they thought they were testing full trilinear and in fact they weren't, ... could they?
Would not be the first time...
Does trilinear do anything to help filter out Moire patterns? Have not had a chance to check the article yet...page is loading slow. I can see dithering but Moire as a side effect of lack of full trilinear? Don't buy that one yet.
you know what your irght, trilinear filtering doesn't reduce moire patterns, mipmaping does. the Trilinear filtering jsut makes mipmap transitions better, but...maybe with lack of good triliniear filtering moire patterns become more apperent? ...hmmm....
Would not be the first time...
show me a site, where, they were complaining about At's trilinear filtering just to make news, ab=nd give me hard facts to prove that they're just whining not to inform their visitors, but to gernerate more hits
so far on this thread we've come to these results,
1. The Russian review if full of shift when they're talking about moire patterns, heck maybe they're making stuff up too to get more hits.
2. It's not Ati's fault they didn't volunteer the information about their filtering, it's the reviewers faults for not comparing the cards at equal IQ.
3. Review sites don't get upset when companies mislead them, they're just complaining to make news, heck it's all about hits right?
4. and Iraq is harboring weapons of mass destruction.
you guys are brilliant, and you should be in politics. :)
jbirney
05-25-04, 04:47 PM
you know what your irght, trilinear filtering doesn't reduce moire patterns, mipmaping does. the Trilinear filtering jsut makes mipmap transitions better, but...maybe with lack of good triliniear filtering moire patterns become more apperent? ...hmmm....
jarred,
thats what I was getting at. I am not saying that there will never be an IQ difference, just that Moire patterns are different form of alasing and tril-linear was not set to handle that issue. I can see where more banding would be present but that Moire claim made me think twice....
Lfctony
05-25-04, 05:05 PM
Iraq is harboring weapons of mass destruction.
What a way to finish a point! :)
Heres the Article Translated
--- START OF ARTICLE ---
Introduction
Recently questions started arising more often about realization of texture filtering in GPUs. One would assume that with current GPU functionality such a basic function as filtering would be performed perfectly, yet the manufactures had the tendency to cut corners ever since the early days of 3D. With current budget (which is more than hundreds of millions) it is possible to perform perfect texture filtering.
But, it appears that in some cases furter approximation of "perfect" does not return what is expected. Our friends at 3dcenter.org were the first to notice it. nVidia in the entire NV3x generation used "optimized" trilinear filtering. But recently it turned out that ATI used similar "optimization" in its new chips beginning with RV3x0 up to the latest R420.
Purpose of this article is to demonstrate and to analyze differences in the realization of trilinear filtering between ATI and NVIDIA in their high-quality and optimized mode of the last generation of chips R420 - Radeon X800 and NV40 - GeForce 6800, respectively.
Let us first familiarize with some terms:
Trilinear filtering (trilinear MIP mapping) - further improvement of bilinear filtering with MIP mapping. Weighted mean value between the results of two bilinear samples from adjacent MIP-levels of texture is the result of trilinear filtration. Depending on the relationship of the sizes of pixel/texel, value of one of the two bilinear samples predominates. This method prevents flickering and sharp change of the clearness of textures during camera motion relative to objects.
I must repeat, that this article will not investigate differences in the bilinear and anisotropic filtering, but only special features of the realization of trilinear filtering.
Excluding insignificant details in this case, trilinear filtering depends on computation of two values Rho(1) and Lambda(2) [look at the original article for formulas].
The formulas given above are taken from OpenGL specification. Although it is evident that Lamda directly depends on Rho, this article will use these two values simultaneously, and from further material it will become clear why. Rho is scale factor, and Lamda is level of detail - LOD.
The final value of color Tau is calculated as linear interpolation between the values of the color, selected from two MIP levels, integer part of Lamda is used to determine from which MIP levels to select color values, and the fractional part of Lamda is the coefficient of interpolation. Everything that we should know about the formula (1) by which Rho is determined, is that resulting value depends on the area of texture, which maps to one pixel of final image.
Our regular visitors have already seen similar images [look at the original article for images] many times. Such images are obtained as a result of rendering of the infinite cylindrical tunnel, whose walls are painted with the aid of a special texture. Special feature of this texture is that it consists of MIP levels where every subsequent level has different color. What is the point of those images? With one look at them it is possible to determine the level of filtering 3D accelerator uses with different level of texture magnification/reduction, isotropic/anisotropic imposition of the textures, and also to determine dependance of filtering level on angle at which textures are superimposed. And all that could be determined with only one image! Hmm... at least it was possible until recently.
...[explanation of what can be seen on the picture, not too relevant so I snipped it out]
The form of the lobes, shown on the picture above, depends on the method, by which Scale factor Rho is calculated. In the case of trilinear filtering, colors on the picture must blend smoothly.
In the article below we will show similar pictures which use somewhat simplified textures - in it all MIP levels will be white, with exception of 2 according to the degree of detailing, which are painted red. On such texture is evident, perfect evident, in what places will that MIP level be used, and how trilinear interpolation between the adjacent MIP levels occurs.
All images and results are obtained with the aid of program TextureFilteringTester developed in iXBT, which makes it possible to investigate the qualitative and speed characteristics of the algorithms of texture filtering, carried out by 3D accelerators.
So, lets see how does the image look like, in the case of high-quality (not optimized) trilinear filtration on ATI R420 and NVIDIA NV40. Each picture below is hyperlinked to larger (uncompressed) PNG version.
How the images were obtained? On NVIDIA NV40 for obtaining the image of the non-optimized trilinear filtering optimization was turned off from the control panel.
ATI at the moment uses more drastic technology of the on/off control of the optimization of trilinear filtering. When the texture is loaded driver analyzes the differences between MIP levels of texture, and if it decides that the less detailed MIP levels are not the reduced copy of previous, then the optimization of trilinear filtering is turned off and the standard method of filtering is used for this texture.
Therefore for obtaining the images with the optimized trilinear filtering, driver was deceived by using special texture. In the course of experimenting with different textures it became clear that ATI includes the optimization of trilinear filtering only for certain class of textures - depending on their description by application. For example, in DirectX textures can belong to one of the three classes: static, dynamic and managed. Optimized trilinear filtrering in the current version of driver is included only for managed textures.
What immediate conclusion can be made from the comparison of the images given above? To the naked eye, completely white and completely red regions increase approximately equally in both chips with the start of the optimized trilinear filtering. It is also evident on the images obtained from R420 that banding occurs, whereas color blending is exceptionally smooth on NV40.
Let us show you the image obtained on reference rasterizer RefRast, which forms part of DirectX SDK.
It is evident that the image obtained with RefRast coincides with the image obtained on R420 with the optimization of filtering turned off. As a convenience for our readers we have made difference images using Photoshop. As a result different types of filtering became visible to the naked eye and at the same time it is possible to compare the behavior of different chips. The first conclusion is that the changes in the trilinear filtering on all chips do not depend on the angle at which textures are superimposed. Another obvious conclusion is the almost completely identical result of the filtering carried out with R420 and RefRast.
Let us look at what happens in real life. Below Are four graphs created according to the experimental data on two for each of the chips R420 and NV40. One of the graphs shows the dependence of the used coefficient of trilinear interpolation on Rho, and another on Lamda (see formulas and description at the beginning of the article). Two curves, for the standard trilinear filtering and for optimized, are presented for each of the graphs as well as one for RefRast.
Thus, it is possible to explain why making of two graphs for each of the chips was necessary. It is evident that the linear interpolation carried out by ATI and NVIDIA chips is based on different variables. ATI uses Rho, and NVIDIA Lamda. This becomes obvious, if we look at what point the coefficient of interpolation is equal to 1/2. For ATI this coefficient becomes equal to 1/2 with Rho = 1.5, and for NVIDIA with Lamda = 0.5. It is also evident that chip ATI in non-optimized mode carries out trilinear interpolation equivalent to DirectX RefRast, we will get back at that soon.
Lets analyze graphs:
- It is obvious that NVIDIA in the standard (non-optimized) mode carries out trilinear filtering ideally close to OpenGL specification OpenGL (at least for 32 bit textures).
- ATI in the standard mode uses high weight coefficients for more detailed MIP-levels.
- NVIDIA in its optimized trilinear filtering uses only bilinear filtering in the range of ±0.16 from the entire value of Lamda (LOD).
- ATI in its optimized trilinear filtering, uses bilinear filtering in the section which represents approximately 30% of entire range, and that section is located on the side where more detailed MIP-levels are used.
Basis on those assertions it is possible to draw the following conclusions:
(a) the percent relationship of the sections where ATI and NVIDIA "optimize" and where only bilinear filtering is used is practically equal
(b) both with standard and with optimized trilinear filtering, images obtained with ATI chips will sometimes appear clearer, and the images, obtained on NVIDIA chips more smeared, but during the camera motion images obtained with ATI chips are more susceptible to moire and sand-like effects (dithering), that appear as a result of under-filtering.
Now let return to the analysis of the graphs obtained on R420 and RefRast. We can note two things: stair-like graph shape, and the linear dependence of the coefficient of interpolation on Rho, and not on Lamda as OpenGL specification recommends.
The stair-like form of graph is caused by the fact that DirectX requires only 5-bit accuracy for the coefficient of interpolation. As I already mentioned above, this was first noticed by our friends from 3DCenter.org. And although I would like that trilinear interpolation is carried out with larger accuracy, DirectX specifications do not require this and vendors are free to do whatever they want as long as they meet the specification.
Let us examine the second thing - the nonlinear dependence of the coefficient of trilinear interpolation on Lamda. What does that mean? The point is that the logarithm calculation is demanding operation and requires large number of transistors. That is why the approximate calculation is used [see formula in original article]
Then it is possible to derive x from Rho exponent, and y from its mantissa. Specifically, this optimization is used both in RefRast and in ATI chips.
Conclusion
I won't go deeper into the analysis of the quality of the trilinear filtering because in this situation its importance is subjective. Specifications that describe optimal algorithms for filtering do exist and they haven't changed, but they are numerous so vendors cannot implement every one of them.
But as GPUs become more productive and powerful the greater becomes the desire to use them as co-processors for arbitrary calculations and tasks. In that area, strict conformance to the specifications is more often a requirement than just a wish. Examples of GPU use can be found on www.gpgpu.org.
--- END OF ARTICLE ---
wow thanx dude, I also think that people should check out the images provided on the site, (uncompressed png format)
Lfctony
05-26-04, 04:12 PM
wow thanx dude, I also think that people should check out the images provided on the site, (uncompressed png format)
Thank God you changed your avatar, everytime I looked at it, it reminded of a martial arts movie and someone getting kicked in a specific place! :)
RobHague
05-26-04, 04:48 PM
Was just looking on Rage3d and someone posted this link, of course.
Giving up on the translation provided by google - Aparentley (so they are saying) the russian's disabled the detection for the optimization so ti applied it 100% of the time, so even when the algorithm wouldnt (as it would make the IQ worse)... if thats so i hardley think the 'tests' they have done are valid.
Id rather see these optimizations turned off, and made sure they are turned off on the 6800 too and then running the benchmarks again.
Was just looking on Rage3d and someone posted this link, of course.
Giving up on the translation provided by google - Aparentley (so they are saying) the russian's disabled the detection for the optimization so ti applied it 100% of the time, so even when the algorithm wouldnt (as it would make the IQ worse)... if thats so i hardley think the 'tests' they have done are valid.
Id rather see these optimizations turned off, and made sure they are turned off on the 6800 too and then running the benchmarks again.
I can't find where that was mentioned in the article, can you point it out?
oh! are you talking about the nv40? yes, it wold appear if that is indeed true that it's not a good comparision, but, you can still come the the same conclusion that the article is stating Ati's filtering has IQ degration
NightFire
05-26-04, 06:29 PM
Yes, I agree. Jarred, your other avatar was freaking me out:p
Yes, I agree. Jarred, your other avatar was freaking me out:p
I thought it was damn funny. :)
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