About
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 in terms of both the image quality at a given bitrate, and the format and bitrate flexibility available to content creators. This allows more assets to use compression, often at a reduced bitrate compared to other formats, reducing memory storage and bandwidth requirements.
Read the ASTC Format Overview for a quick introduction to the format, or read the full Khronos Data Format Specification for all the details.
License
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
exhaustive, thorough, medium, fast, and fastest encoding quality
presets.
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 astcenc compressor supports generation of images for all three profiles
allowed by the ASTC specification:
- 2D Low Dynamic Range (LDR profile)
- 2D LDR and High Dynamic Range (HDR profile)
- 2D and 3D, LDR and HDR (Full profile)
It also supports all of the ASTC block sizes and compression modes, allowing content creators to use the full spectrum of quality-to-bitrate options ranging from 0.89 bits/pixel up to 8 bits/pixel.
Prebuilt binaries
Release build binaries for the astcenc stable releases are provided in the
GitHub Releases page.
Latest 3.x stable release: 3.6
- Change log: 3.x series
Latest 2.x stable release: 2.5
- Change log: 2.x series
Binaries are provided for 64-bit builds on Windows, macOS, and Linux. The builds of the astcenc are provided as multiple binaries, each tuned for a specific SIMD instruction set.
For x86-64 we provide, in order of increasing performance:
astcenc-sse2- uses SSE2astcenc-sse4.1- uses SSE4.1 and POPCNTastcenc-avx2- uses AVX2, SSE4.2, POPCNT, and F16C
The x86-64 SSE2 builds will work on all x86-64 machines, but it is the slowest of the three. The other two require extended CPU instruction set support which is not universally available, but each step gains ~15% more performance.
For Apple silicon macOS devices we provide:
astcenc-neon- uses NEON
Repository branches
The main branch is an active development branch for the compressor. It aims
to be a stable branch, but as it is used for ongoing development expect it to
have some volatility.
The 2.x branch is a stable branch for the 2.x release series. It is no longer
under active development, but is a supported branch that will continue to get
backported bug fixes.
The 1.x branch is a stable branch for the 1.x release series. It is no longer
under active development or getting bug fixes.
Any other branches you might find are development branches for new features or optimizations, so might be interesting to play with but should be considered transient and unstable.
Getting started
Open a terminal, change to the appropriate directory for your system, and run the astcenc encoder program, like this on Linux or macOS:
./astcenc
... or like this on Windows:
astcenc
Invoking 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 -cl \ -cs \ -ch \ -cH modes. For example:
astcenc -cl example.png example.astc 6x6 -medium
This compresses example.png using the LDR color profile and a 6x6 block
footprint (3.56 bits/pixel). The -medium quality preset gives a reasonable
image quality for a relatively fast compression speed, so is a good starting
point for compression. The output is stored to a linear color space compressed
image, example.astc.
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 -dl \ -ds \ -dh \ -dH modes. For example:
astcenc -dh example.astc example.tga
This decompresses example.astc using the full HDR feature profile, storing
the decompressed output to example.tga.
The modes available mirror the options used for compression, but use a d
prefix. 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 -tl \ -ts \ -th \ -tH modes.
For example:
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 mirror the options used for compression, but use a t
prefix.
Experimenting
Efficient real-time graphics benefits from minimizing compressed texture size, as it reduces memory footprint, 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 -fastest, through -fast,
-medium and -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.
Documentation
The ASTC Format Overview page provides a high level introduction to the ASTC texture 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 astcenc.
It covers:
- 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 .astc File Format page provides a light-weight
specification for the .astc file format and how to read or write it.
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.
Support
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 © 2013-2022, Arm Limited and contributors. All rights reserved.