Image Quality Analysis Fall 2003: A Glance Through the Looking Glass

Final Words

Making useful sense of all this information is tricky at best.

There is no real-time 3D engine or hardware in existence that does everything the “right way” to all things visible all the time. In order to affect real-time 3D rendering, trade-offs must be made. Only when these trade-offs become highly perceptible are they a problem.

It is the GPU makers' responsibility to implement optimizations in ways that don't negatively impact the image quality of a scene, but there really isn't a way to quantitatively make a decision about any given optimization. That which is acceptable to one person may not be acceptable to another, and it is a tough call to make.

One stop gap is the end user community's perspective on the issues. If it is decided that a particular optimization shouldn't be done by the people who own (or potentially own) a particular card, it is in the GPU makers' best interest to make some changes.

It is in game developers' best interest to work with GPU makers to keep image quality top notch for their game's sake. In fact, rather than concentrating on getting raw frame rate to the end user, IHVs should focus on getting powerful and easy-to-use features to the developer community. So far, ATI has a leg up on ease of use (developers have said that programming has gone quickly and smoothly with ATI cards with NVIDIA code paths taking longer to tweak), while NVIDIA's hardware offers more flexibility (NVIDIA allows much longer shader programs than ATI and offers functionality above the minimum of current APIs). At this point, ATI is in a better position because it doesn't matter if NVIDIA offers more functionality, if the only code that can take advantage of it runs incredibly slow after taking a very long time to develop. Hopefully, we will see more flexibility from ATI and fewer nuances in how programs need to be written from NVIDIA in next year's hardware.

At this point, ATI uses a more visually appealing algorithm for antialiasing, while NVIDIA does a better job calculating texture LOD and does more alpha blending. The question we are asking now is whether or not these optimizations degrade image quality in any real way. We feel that NVIDIA needs to refine its antialiasing algorithms, and ATI needs to do a better job of rendering alpha effects. We are still looking into the real world effects of the distance calculations that ATI uses in determining LOD, but the problem definitely manifests itself in a more subtle way than the other two issues that we have raised.

The decision on what is acceptable is out of our hands, and we can't really declare a clear winner in the area of image quality. We can say that it appears from the tests we've done that, generally, NVIDIA hardware does more work than ATI. Honestly, it is up to the reader to determine what aspects of image quality are important, and how much of what we covered is relevant.

We really don't have a good way to compare pixel shader rendering quality yet. The possible issues with different shader implementations have yet to be seen in a game, and we hope they never will. It is a developer's responsibility to create a game that gives a consistent experience across the two most popular GPUs on the market, and both ATI and NVIDIA have the ability to produce very high quality shader effects. Each architecture has different limitations that require care when programming, and we will still have to wait and see whether or not there will be image quality differences when more DX9 games hit the shelves.

For now, we are committed to bringing to light as much information as possible about image quality and optimizations in graphics hardware. Armed with this information, individuals will be able to come to their own conclusions about which optimizations go too far and which serve their intended purpose. We hope that all the details that we have brought to light have served their purpose in helping our readers to make informed decisions about graphics hardware.