• Page
• Discussion
• View source
• History

From Odwiki

RAT files are a special image format used by Houdini to store MipMap texture images. RAT stands for "Random Access Texture" file.

RAT files are Paged, meaning that only portions of the file are loaded into RAM at one time.

RAT files are also MipMapped, meaning they are pre-filtered to perform adequate TextureFiltering, at the negligible cost of a slightly larger file size.

The environment variable HOUDINI_RAT_USAGE can be used to specify how many Mb of RAT files can be in memory at a single time. At the current time, this defaults to 32Mb, meaning that regardless of the resolution of the image, or how many texture files are used, only 32Mb will be used for texture map storage. As of Houdini 9.5+, it's prefered that you set this with the appropriate RenderingParameter.

RAT files will produce much better anti-aliased images than any other format of image since much better TextureFiltering is performed. This will help mostly with high-frequency texures (highly detailed).

RAT files share many of the same features as Houdini's pic file format, including DeepRaster layers, 8/16/32-bit floating point precision, etc.

RAT files can also be the kind of "deep", as in "deep shadow map"-- where a single pixel can store values at multiple depths. When used from lights to record deep opacity, these are called "Deep Shadow Maps (DSMs)". When used from a Camera to store multiple planes of image data (as in the DeepRaster planes mentioned above) at multiple depths, these are called "Deep Camera Maps (DCMs)".

Mantra will convert any of the other specified formats it can read to RAT format internally in order to produce higher quality images which exhibit better filtering. However, note that since this is all stored in RAM, you won't benefit from the Paged nature of this format. You can use icp or iconvert or COPS to convert to a RAT file on disk.