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3Dc: Get the Speed, Admire Under Microscope

Unlike HDR, do not expect normal map compression that is sometimes referred as 3Dc to make any huge difference in image quality in FarCry. 3Dc, however, improves performance in addition to some potential minor image quality gains.

So, what is 3Dc and Normal Maps Compression?

Normal maps are a new step in the bump mapping techniques, and today they get more and more popular. The idea behind the use of normal maps implies that the information about the object surface is stored as a texture, where each texture element saves three components of a vector perpendicular to the object surface in a given point, i.e. of the normal vector.

ATI RADEON, NVIDIA GeForce Normal Map Compression

 

Normal Maps Compressed

Normal Maps Not Compressed

ATI RADEON:
NVIDIA GeForce:

The use of normal maps allows obtaining a much more detailed and realistic image, without increasing the number of polygons used to build it. As a result, normal maps can be created from the difference between the high-polygon model and simple model of the object. Later on you can use only the simple model, but the normal map you apply to it will make it look almost as good as the reference image.

Usually, normal maps describing the object surface are applied together with the base textures storing the color info about the object. The higher is the level of details for the textures and normal maps, the more realistic the image will look. However, the use of textures and high resolution normal maps increases the memory bus workload that is why some alternative solutions are necessary to retain high level of performance. DirectX 9 offers a set of DXTC algorithms providing efficient texture compression, and despite the info losses during compression manage to retain the acceptable texture quality. However, the compression of normal maps cannot be done with DXTC algorithms, because the sharp changes of the normal vector get lost as a result of compression and we get block artifacts instead.

The 3Dc algorithms supported by ATI RADEON X800 on the hardware level is intended for normal maps compression and causes not such a great worsening of the image quality. When we use normal maps compressed with 3Dc algorithm, RADEON X800 stores them in the graphics memory and transfers to the VPU compressed, decompressing them “on the fly”. The restoring of the third normal vector component in the pixel shader doesn’t take too much of the resources: just a few additional instructions should be added to the shader in this case.

The main thing you should now about 3Dc is when we compress dual-component normal maps, 3Dc ensures data compression with 2:1 ratio. The overall compression including the shift from the regular vector description to the dual-component description is done with the ratio of 4:1.

FarCry and Compression of Normals

Since currently NVIDIA does not have any algorithms specifically intended to compress the normal maps, Crytek only implemented normal maps compression technology for ATI’s RADEON X800 product line. While you can enable normal map compression by typing “r_TexNormalMapCompressed 1” in the console or adding the same key to the shortcut of the game on the GeForce FX, GeForce 6 and RADEON 9000-series hardware, this will not be true normal compression, but just the usage of a 2-component texture which picks up the idea of re-calculating the Z-Value using a pixel shader.

ATI RADEON, NVIDIA GeForce Normal Map Compression

 

Normal Maps Compressed

Normal Maps Not Compressed

ATI RADEON:
NVIDIA GeForce:

Unfortunately, Crytek did not add any new normals to the game, therefore, there hardly any eye-candy improvements.

 
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