Sapphire Radeon X850XT PE AGP 7

Sapphire Radeon X850XT PE AGP Review

Description & Installation »


3Dc is a technology that ATI developed under the aim of providing better image quality. How does it work? All games have to use some sort of texture compression, because the textures would simply be too big to fit into you video card’s memory. Direct X has DXTC compression, whereas 3Dc is a new form of compression, resulting in better textures. Let’s have a look at a picture so I can show you what I mean:

The details of the picture on the right are far better that those on the left. Normal maps are used, they are special textures that add detail to 3D objects. Normal maps allow the card to determine the direction in which incoming light will reflect off a surface at any given point. To create a Normal map, a high polygon count and a low polygon count model is used. The two models are compared, and the Normal map is created. The Normal map is then used on the low polygon count model. This way, the low polygon count model looks realistic, with fine details.

3Dc comes into all of this, as it is used to compress the Normal maps, so that they can be applied to the models, thereby adding detail. The difference between 3Dc normal map compression and DXTC (Direct X texture compression) can be seen below

3Dc is not perfect - it is what we call a lossy form of compression. Lossy means that some of the data that is input (in this case the normal map data) is lost during compression and decompression. This means that some detail is lost, but compared to lossless compression (where no information would be lost), the size of the map is much smaller.

3Dc compresses normal maps, therefore it allows more maps with more details to be stored in the 3d card's memory, without exceeding the onboard memory limit.
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