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Page: Using Basis Universal to decompress any supported GPU texture format
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.basis File Format and ETC1S Texture Video Specification .basis Format Forwards and Backwards Compatibility .basis file format overview ASTC HDR 6x6 Example Images ASTC and XUASTC LDR Usage Guide Compressor Definitions and Classes DDS Transcoder Displaying .astc file block statistics using the peek command line option ETC1S Compression Effort Levels ETC1S Encoder Speed Encoding ETC1S and XUASTC LDR Texture Video GPU Textures as Derived (Compiled) Data GPU Textures as Universal Latents Home How to Deploy ETC1S Texture Content Using Basis Universal How to Use and Configure the Transcoder How to benchmark or directly call the UASTC functions without using .basis JPEG for ASTC KTX2 File Format Support Technical Details for basisu v2.0 KTX2 File Format Support Technical Details for basisu v2.1 KTX2 File Format Support Technical Details LICENSE Legal IP License Information List of Available Software ASTC Decoders NOTICE OpenGL texture format enums table Pure C API Common Definitions Pure C API Compression Pure C API Transcoding Release Notes Shader and In Loop Deblocking Sponsors and Supporters The Three Generations of GPU Texture Distribution Transcoder Debugging Transcoder Internals Analytical Real Time Encoders and Transcoders Transcoder Internals Analytical Real Time Encoders Transcoder Module Definitions and Classes Transcoder Texture Format Support for ETC1S and UASTC LDR 4x4 UASTC HDR 4x4 Texture Specification UASTC HDR 6x6 Intermediate File Format (Basis GPU Photo 6x6) UASTC HDR 6x6 Support Notes UASTC HDR Examples UASTC LDR 4x4 Implementation Details UASTC LDR 4x4 Texture Specification Using Basis Universal to decompress any supported GPU texture format Very early HDR 6x6 examples XUASTC LDR Arithmetic Profile XUASTC LDR Endpoint Conversion for DPCM Prediction XUASTC LDR Range Coding XUASTC LDR Specification v1.0 XUASTC LDR Weight Grid DCT XUASTC LDR log_astc_block Structure XUASTC LDR XUBC7 File Format XUBC7 Low Level Format XUBC7 Usage Guide basisu.exe Command Line Tool Options
35 Using Basis Universal to decompress any supported GPU texture format
Rich Geldreich edited this page 2026-02-11 22:03:58 -05:00
Table of contents

The Basis Universal encoder/transcoder libraries contain easy to use functions to unpack the following standard compressed GPU texture formats:

Full support:

  • ASTC - Full specification, any block size, LDR/HDR, all standard ASTC decode profiles (linear vs. sRGB etc.), 9E5 support, logical and physical block packing and unpacking, CEM decoding, BISE quant/dequant, optimized partition pattern subset index calculation, faster XUASTC LDR-only block decoding, fuzzed, two full low-level decoders (for correctness checking): See the stand-alone header library transcoder/basisu_astc_helpers.h or encoder/3rdparty/android_astc_decomp.h. Fuzz compared vs. ARM's decoder in astcenc.
  • BC7 - Fully specification, in transcoder .cpp module, see transcoder/basisu_transcoder_internal.h, low-level function basist::bc7u::unpack_bc7().
  • BC6H - Full specification (signed or unsigned variant), in encoder library.
  • BC1-5 - Full format
  • ETC1 - Full format
  • ETC2 EAC R11/RG11 - Only unpacks to 8-bit/channel
  • PVRTC1 4bpp RGB/RGBA - Decompression has been verified against PVRTexTool's output for correctness.
  • ATC RGB/RGBA

Limited support (just what we encode to):

  • ETC2 RGB/RGBA8 - Only supports ETC1 for color data (no planar, T/H modes). EAC alpha data is fully supported
  • PVRTC2 - Limited support: Just the non-interpolated mode our transcoders use.
  • FXT1 - Limited support: just the specific BC1-like mode we use

Before you can unpack textures, be sure to call basisu_encoder_init() once at startup.

To unpack individual 4x4 (or 8x4 for FXT1) texel blocks to raw RGBA pixels, use one of these functions declared in encoder/basisu_gpu_texture.h:

bool unpack_block(texture_format fmt, const void *pBlock, color_rgba *pPixels, bool astc_srgb);
bool unpack_block_hdr(texture_format fmt, const void* pBlock, vec4F* pPixels);

This doesn't work on PVRTC1 textures, because the decoder needs access to the surrounding blocks. Alternately, you can create a basisu::gpu_image object, then call gpu_image::unpack() or gpu_image::unpack_hdr(). This works on any supported format, including PVRTC1.