AMD Radeon HD 7870 & HD 7850 Review

Author: SKYMTL
Date: March 3, 2012
Product Name: Radeon HD 7870 & HD 7850
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Advanced Image Quality

Much has been said about AMD’s claims of leading edge texture filtering quality on the HD 6000-series but for the most part, it was an improvement over previous generations. Whether it was up to expectations is still open for debate but the Southern Islands family is once again claiming to have virtually eliminated the flickering and artifacts that sometimes appear in games.

In order to high the high note in terms of texture filtering, Southern Islands cards feature an improved anisotropic filtering algorithm that’s designed to virtually eliminate shimmering in high resolution textures. This may sound like a tall order to fulfill but after seeing it in action, we’re confident AMD can deliver this time around.

One of the beauties of this new filtering algorithm is its ability to run without additional buffering so there is no drain on system resources. In addition, it is automatically enabled to gamers should see vastly improved image quality without having to dive into the Catalyst Control Panel.

Introducing PRT (Partially Resident Textures)

One of the main challenges for today’s GPUs is how to handle large amounts of high resolution textures when moving through a scene. Presently, when a player moves through a game environment the texture information in upcoming frames is constantly loaded between the disk, CPU and the graphics card. Usually the effect of this preloading is seamless but as larger amounts of information are loaded, stuttering can occur.

AMD’s solution to this somewhat complex problem is to leverage the local memory on the GPU and allow it to act as a true texture caching system. Essentially, upcoming textures are prefetched from the CPU and disk and stored locally on the GPU until they are ready to be used by the application. In a way this can almost be considered a form of texture “streaming” and should help eliminate the stutter normally associated with scene loading.

In addition to preloading, PRT can also dynamically load selected textures based on when they will be needed instead of loading every bandwidth-hogging texture all the time. This should help eliminate the memory footprint the feature requires.

Unfortunately for gamers Partially Resident Textures technology is application controlled so it has to be built into a game engine before it can be utilized. Supposedly, AMD’s development team is working with game developers to include this feature in upcoming releases but there aren’t any titles on the horizon that will put it to good use.

New Anti Aliasing Modes: MLAA 2.0 & SGSSAA

Morphological AA or MLAA was introduced by AMD back when the HD 6870 was first announced. In a nutshell it is form of fullscreen anti-aliasing that delivers an image quality which is comparable to Super Sample AA, but can be implemented with a fraction of SSAA’s performance hit. The AA algorithms are calculated more efficiently by leveraging GPGPU compute abilities alongside Microsoft’s DirectCompute API. Since the post-processing filtering is done by DirectCompute, the whole scene can be quickly analyzed so this AA method isn’t limited to only certain aspects of a given image. One of the more interesting benefits of Morphological AA being done through a standalone API is the fact that it can be used for both 2D and 3D scenes. Thus, it can be applied to things like video, Flash apps and more. In addition, since it is controlled directly through AMD’s Catalyst Control Center and makes use of DirectCompute, Morphological AA has the ability to be forced in any DX9, DX10 or DX11 game.

Unfortunately, one of the tradeoffs was lower performance but with the introduction of MLAA 2.0, quality has been slightly improved while system resource requirements have been minimized. The result should be better image quality without a significant impact upon in game performance.

Starting in the 12.3 beta due out later this month, AMD will be including yet another anti aliasing routine into their Catalyst Control Center’s bag of tricks. Sparse Grid Supersampling Anti Aliasing or SGSSAA has been a hot topic on game developer boards since it allows for ultra high image quality through the use of advanced AA techniques.

In layman’s terms, SGSSAA is meant to calculate each individual frame as a whole as opposed to MSAA’s method of analyzing polygonal edges and applying a simple AA mask. Not only does this approach allow for a dynamic level of detail but all elements of a scene receive anti aliasing which includes textures, polygon edges, shadows and shader modules. Unfortunately, these types of calculations take a massive amount of horsepower but the tradeoff should be some of the most realistic in game scenes we’ve experienced.

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