Today's Hard|Forum Post
Today's Hard|Forum Post

AMD Morphological AA Performance and IQ Review

We take an in-depth look at AMD’s new Morphological AA technology introduced with the Radeon HD 6870 and Radeon HD 6850. We will evaluate performance and image quality with the new antialiasing feature. This new feature is poised to provide an improved gameplay experience.

Introduction

On October 21st AMD released its next generation performance mainstream graphics processors, the new Radeon HD 6870 and Radeon HD 6850. There was a new piece of technology attached with that release called Morphological AA which we wanted to dedicate a full article's worth of coverage to. A whole "new" way of doing AA! Does it work? Does it work well? And do we have the shader power to pull it off and actually game at expected quality levels?

Morphological Anti-Aliasing

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(The second slide reads: "Detect high contrast edges" "Compute coverage")

The first thing you need to know is that this is a post-processing effect that is applied to the output image after all rendering stages. What this means is that the video card driver applies a custom post-processing filter to each frame after it goes through the GPU pipeline, and before it is displayed on your monitor. This is performed via DirectCompute accelerated by the video card shaders. This is not like in-game antialiasing where 2X MSAA, 4X MSAA or 8X MSAA are performed during the rendering of the scene through the pipeline. By doing it this way, Morphological AA is able to be applied to the entire image, full-screen, so that any aliasing on the image can be reduced, no matter where the textures or polygons are. This is somewhat like applying a filter in Adobe Photoshop.

Our new morphological anti-aliasing technique works as a post process effect. In other words, we finish rendering each frame normally, but before presenting it to the display; we run it through another shader pass to perform the filtering. This differs from traditional multi-sample and super-sample AA techniques where the filtering occurs during the rendering of each frame. In fact, this technique can eliminate aliasing for still images, though it’s intended to work better when in motion.

The filter works by first detecting high contrast edges with various pixel-sized patterns that are normally associated with aliasing, and assumes they should actually be straight lines that are not aligned to pixel edges. It then estimates the length and angle of the ideal line for each edge, and determines the proportional coverage by the lighter and darker color for each pixel along the edge. Finally it uses this coverage information to blend the colors for each pixel.

This new feature promises improve image quality, reducing aliasing, comparable to Supersampling AA but with a lesser performance hit. This new antialiasing feature is compatible with all other AMD antialiasing settings and does not require specific game support to function. This feature should be able to work on any game, even if the game does not have built in antialiasing control and even if the game is based on deferred rendering in DX9. This means those games that don’t support AA now have a method that will anti-alias them!

Not Screenshot Compatible

AMD has provided a utility that runs the same code as the driver on screenshots to filter them just like they would look in-game with Morphological AA enabled. It is this utility we have to use to show you image quality comparison today because of the nature of post-processing, it cannot be captured from a FRAPS screenshot. Meaning, if you take a screenshot in-game with Morphological AA enabled, it will not show up in your screenshot. The utility takes the non-antialiased screenshot and applies the code from the driver that is applied in your games, to produce Morphological AA filtering on the image. This way, we can show you exactly what you will see in your game when you apply Morphological AA.

Driver Control

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Here is how to use Morphological AA. In the driver control panel, you simply enable the check-box labeled Morphological AA. That’s it. Now Morphological AA will be enabled in all your games. This feature is independent of other AA settings, including MSAA. Meaning, you do not have to have 2X MSAA, 4X MSAA or 8X MSAA enabled in-game or forced from the control panel for Morphological AA to work. In fact, you should disable AA in the game or turn it off completely; "No AA." With AA turned off in the game, then you can turn Morphological AA on and it will be applied in the game.

Bug in Catalyst 10.10c Hotfix

We are using Catalyst 10.10c Hotfix driver in our testing. We did experience a bug in our testing with Radeon HD 6850 and Radeon HD 6870. Apparently, we could not get Morphological AA to work with any DX10 or DX11 game, despite the fact that it should work. We found that it worked flawlessly in every DX9 game we threw at it. A quick reply from AMD revealed that there is a current bug in Catalyst 10.10c Hotfix driver that makes it so that even if Morphological AA is checked, it isn’t actually turning on in like it should.

"Thanks for bringing this to my attention. I brought it to the Catalyst engineers. They quickly identified that intermittently the setting in CCC doesn't stick 100% of the time for some odd reason. We will have an update for Catalyst 10.10c on Monday (or Tuesday the latest) to resolve this."

This seems to have been updated now, but too late for it to be included in this article. Nevertheless, we get a great look at what MorphAA does for the gamer today.

For our testing today, we are going to use a DX9 game that worked flawlessly and allowed us to look at performance and image quality easily. We chose F1 2010, which is based on the DiRT 2 gaming engine, and will support DX11 in a future patch. This game gives a very even level of performance and it is very easy to look at and compare performance on a graph. This game also performs very well, and uses shaders and textures, so we can see how much of a performance hit Morphological AA incurs. We are also able to look at polygon aliasing image quality, transparency image quality and shader aliasing with this game. We will of course continue to use Morphological AA (MLAA) in all future retail video card evaluations.