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richgel999 authored Apr 13, 2021
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Expand Up @@ -20,9 +20,11 @@ For v1.13, we've added numerous ETC1S encoder optimizations designed to greatly

[Release Notes](https://github.com/BinomialLLC/basis_universal/wiki/Release-Notes)

### Usage Information
### Quick Introduction

Probably the most important concept to understand about Basis Universal before using it: The system supports **two** very different universal texture modes: The original "ETC1S" mode is low/medium quality, but the resulting file sizes are very small because the system has built-in compression for ETC1S texture format files. This is the command line encoding tool's default mode. ETC1S textures work best on images, photos, map data, or albedo/specular/etc. textures, but don't work as well on normal maps. There's the second "UASTC" mode, which is significantly higher quality (near-BC7 grade), and is usable on all texture types including complex normal maps. UASTC mode purposely does not have built-in file compression like ETC1S mode does, so the resulting files are quite large (8-bits/texel - same as BC7) compared to ETC1S mode. The UASTC encoder has an optional Rate Distortion Optimization (RDO) encoding mode (implemented as a post-process over the encoded UASTC texture data), which lowers the output data's entropy in a way that results in better compression when UASTC .basis files are compressed with Deflate/Zstd, etc. In UASTC mode, you must losslessly compress the file yourself.
Probably the most important concept to understand about Basis Universal before using it: The system supports **two** very different universal texture modes: The original "ETC1S" mode is low/medium quality, but the resulting file sizes are very small because the system has built-in compression for ETC1S texture format files. This is the command line encoding tool's default mode. ETC1S textures work best on images, photos, map data, or albedo/specular/etc. textures, but don't work as well on normal maps.

There's the second "UASTC" mode, which is significantly higher quality (comparable to BC7 and highest quality LDR ASTC 4x4), and is usable on all texture types including complex normal maps. UASTC mode purposely does not have built-in file compression like ETC1S mode does, so the resulting files are quite large (8-bits/texel - same as BC7) compared to ETC1S mode. The UASTC encoder has an optional Rate Distortion Optimization (RDO) encoding mode (implemented as a post-process over the encoded UASTC texture data), which conditions the output texture data in a way that results in better lossless compression when UASTC .basis files are compressed with Deflate/Zstd, etc. In UASTC mode, you must losslessly compress .basis files yourself. .KTX2 files have built-in lossless compression support using [Zstandard](https://facebook.github.io/zstd/), which is used by default on UASTC textures.

Basis Universal is not an image compression codec, but a GPU texture compression codec. It can be used just like an image compression codec, but that's not the only use case. Here's a [good intro](http://renderingpipeline.com/2012/07/texture-compression/) to GPU texture compression. If you're looking to primarily use the system as an image compression codec on sRGB photographic content, use the default ETC1S mode, because it has built-in compression.

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