This is the official repository for the Arm® Adaptive Scalable Texture
Compression (ASTC) Encoder,
astcenc, a command-line tool for compressing
and decompressing images using the ASTC texture compression standard.
The ASTC format
The ASTC compressed data format, developed by Arm® and AMD, has been adopted as an official extension to the Open GL®, OpenGL ES, and Vulkan® graphics APIs. It provides a major step forward both in terms of image quality at a given bitrate, and in terms of the format and bitrate flexibility available to content creators. This allows more assets to use compression, often at a reduced bitrate compared to legacy formats, reducing memory bandwidth and energy consumption.
Read our ASTC Format Overview for a quick introduction, or read the full data format specification:
This project is licensed under the Apache 2.0 license. By downloading any component from this repository you acknowledge that you accept terms specified in the LICENSE.txt file.
Encoder feature support
The encoder supports compression of low dynamic range (BMP, JPEG, PNG, TGA) and high dynamic range (EXR, HDR) images, as well as a subset of image data wrapped in the DDS and KTX container formats, into ASTC or KTX format output images.
The decoder supports decompression of ASTC or KTX format input images into low dynamic range (BMP, PNG, TGA), high dynamic range (EXR, HDR), or DDS and KTX wrapped output images.
The encoder allows control over the compression time/quality tradeoff with
fastest encoding quality
The encoder allows compression time and quality analysis by reporting the compression time, and the Peak Signal-to-Noise Ratio (PSNR) between the input image and the compressed output.
ASTC format support
The ASTC specification allows three profiles of implementation:
- 2D Low Dynamic Range (LDR profile)
- 2D LDR and High Dynamic Range (HDR profile)
- 2D and 3D, LDR and HDR (Full profile)
astcenc compressor supports generation of images for all three profiles.
In addition it also supports all of the ASTC block sizes and compression
modes, allowing content creators access the full spectrum of quality-to-bitrate
options ranging from 0.89 bits/pixel up to 8 bits/pixel.
Release build binaries for the
astcenc stable releases are provided in the
GitHub Releases page.
Binaries are provided for 64-bit builds on Windows, macOS, and Linux.
- Latest stable release: 2.2.
- Change log: 2.x series
astcenc 2.x binaries
The current builds of the astcenc 2.x series are provided as multiple binaries, each tuned for a specific SIMD instruction set. We provide, in order of increasing performance:
astcenc-sse2- uses SSE2
astcenc-sse4.1- uses SSE4.1 and POPCNT
astcenc-sse4.2- uses SSE4.2 and POPCNT (deprecated)
astcenc-avx2- uses SSE4.2, POPCNT, and AVX2
The SSE2 builds will work on all x86-64 host machines, but it is the slowest of the three. The other two require extended CPU instruction set support which is not universally available.
It is worth noting that the three binaries do not produce identical output images; there are minor output differences caused by variations in floating-point rounding.
master branch is an active development branch for the compressor. It aims
to be a stable branch, but as it is used for development expect it to change.
1.x branch is a maintenance branch for the 1.x release series. It is
no longer under active development.
Open a terminal, change to the appropriate directory for your system, and run the astcenc encoder program, like this on Linux or macOS:
... or like this on Windows:
astcenc -help gives an extensive help message, including usage
instructions and details of all available command line options. A summary of
the main encoder options are shown below.
Compressing an image
Compress an image using the
-cH modes. For example:
astcenc -cl example.png example.astc 6x6 -medium
example.png using the LDR color profile and a 6x6 block
footprint (3.55 bits/pixel). The
-medium quality preset gives a reasonable
image quality for a relatively fast compression speed. The output is stored to
a linear color space compressed image,
The modes available are:
-cl: use the linear LDR color profile.
-cs: use the sRGB LDR color profile.
-ch: use the HDR color profile, tuned for HDR RGB and LDR A.
-cH: use the HDR color profile, tuned for HDR RGBA.
Decompressing an image
Decompress an image using the
-dH modes. For
astcenc -dh example.astc example.tga
example.astc using the full HDR feature profile, storing
the decompressed output to
The modes available are:
-dl: use the linear LDR color profile.
-ds: use the sRGB LDR color profile.
-dH: use the HDR color profile.
Note that for decompression there is no difference between the two HDR modes, they are both provided simply to maintain symmetry across operations.
Measuring image quality
Review the compression quality using the
-ts \ -
th \ -
astcenc -tl example.png example.tga 5x5 -thorough
This is equivalent to using using the LDR color profile and a 5x5 block size
to compress the image, using the
-thorough quality preset, and then
immediately decompressing the image and saving the result. This can be used
to enable a visual inspection of the compressed image quality. In addition
this mode also prints out some image quality metrics to the console.
The modes available are:
-tl: use the linear LDR color profile.
-ts: use the sRGB LDR color profile.
-th: use the HDR color profile, tuned for HDR RGB and LDR A.
-tH: use the HDR color profile, tuned for HDR RGBA.
Efficient real-time graphics benefits from minimizing compressed texture size, as it reduces memory bandwidth, saves energy, and can improve texture cache efficiency. However, like any lossy compression format there will come a point where the compressed image quality is unacceptable because there are simply not enough bits to represent the output with the precision needed. We recommend experimenting with the block footprint to find the optimum balance between size and quality, as the finely adjustable compression ratio is one of major strengths of the ASTC format.
The compression speed can be controlled from
-thorough, up to
-exhaustive. In general, the more time the
encoder has to spend looking for good encodings the better the results, but it
does result in increasingly small improvements for the amount of time required.
-fastest quality preset is designed for quickly roughing-out
new content. It is tuned to give the fastest possible compression, often at the
expense of significant image quality loss compared to
-fast. We do not
recommend using it for production builds.
There are many other command line options for tuning the encoder parameters which can be used to fine tune the compression algorithm. See the command line help message for more details.
The ASTC Format Overview page provides a high level overview of the ASTC data format, how it encodes data, and why it is both flexible and efficient.
The Effective ASTC Encoding page looks at some of the
guidelines that should be followed when compressing data using
- How to efficiently encode data with fewer than 4 channels.
- How to efficiently encode normal maps, sRGB data, and HDR data.
- Coding equivalents to other compression formats.
The Building ASTC Encoder page provides instructions on
how to build
astcenc from the sources in this repository.
The Testing ASTC Encoder page provides instructions on how to test any modifications to the source code in this repository.
If you have issues with the
astcenc encoder, or questions about the ASTC
texture format itself, please raise them in the GitHub issue tracker.
If you have any questions about Arm Mali GPUs, application development for Arm Mali GPUs, or general graphics technology please submit them on the Arm Mali Graphics forums.
Copyright (c) 2013-2020, Arm Limited and contributors. All rights reserved.