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Basis Universal uses texture compression formats or technologies created by several companies: ARM Holdings, AMD, Ericsson, Microsoft, and Imagination Technologies Limited. All are supported by various open standards or API's from The Khronos Group, such as OpenGL 4.5, OpenGL ES, or Vulkan.

A few texture formats (such as AMD/ATI's ATC texture format, or PVRTC2) were not documented sufficiently by the originator of the format. In these cases, we relied on open source code references from other authors, or information in published articles/papers to implement support for those texture formats in our transcoder. These references are included here.

ASTC usage falls under the astc-encoder Apache 2.0 license.

PVRTC1/2: See the PVRTC Specification and User Guide. Imagination Technologies Limited, 23 Nov 2018. Also see the Khronos Data Format Specification. See PVR Texture Compression Exploration and PvrTcCompressor. Also see Texture Compression Techniques.

ETC1 and ETC2 EAC: See the Khronos Data Format Specification and the OpenGL 4.5 Core Profile Appendix C.

BC1-5,7: Part of Microsoft's Direct3D API technology. See Texture Block Compression in Direct3D 11. Also see the squish library.

ATC: See the OpenGL extension GL_AMD_compressed_ATC_texture. For low-level ATC texture format information, see S3TConv and the paper A Method for Load-Time Conversion of DXTC Assets to ATC.

FXT1: See the OpenGL extension GL_3DFX_texture_compression_FXT1.

Also see Intel(R) Open Source HD Graphics Programmers' Reference Manual (PRM). This reference manual details how to encode FXT1, ETC1, ETC2, EAC, DXT/BC1-3, BC4/5/7, and ASTC.

Basis Universal's KTX2 transcoder and encoder utilize Zstandard, a stable lossless compressed file format defined by IETF RFC 8478. The Zstandard library uses the BSD license and is Copyright (c) 2016-present, Facebook, Inc. We have included copies of the single source file variants of Zstandard in the "zstd" directory to simplify building.