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 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.

The ASTC data format specification is available here:

Khronos Data Format Specification v1.2 # ASTC

License

By downloading any component from this repository you acknowledge that you accept the End User Licence Agreement for the ASTC Encoder. See the LICENSE.md file for details.

Encoder feature support

The encoder supports compression of PNG, TGA and KTX input images into ASTC format output images. The encoder supports decompression of ASTC input images into TGA or KTX format output images.

The encoder allows control over the compression time/quality tradeoff with exhaustive, thorough, medium, fast, and very fast encoding speeds.

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)

The 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.

Prebuilt binaries

Prebuilt release build binaries for Windows (x86 and x64), Linux (x86 and x64), and macOS (x64) are available here:

Binary directory.

These binaries are built from the latest stable tag, and therefore do not necessarily represent the current state of the master branch source code.

Getting started

Open a terminal, change to the appropriate directory for your system, and run the astcenc encoder program, like this on Linux or Mac OS:

./astcenc

... or like this on Windows:

astcenc

Invoking the tool with no arguments gives an extensive help message, including usage instructions, and details of all the available command line options.

Compressing an image

Compress an image using the -c option:

astcenc -c example.png example.astc 6x6 -medium

This compresses example.png using the 6x6 block footprint (3.55 bits/pixel) and a medium compression speed, storing the compressed output in the linear color space to example.astc.

Decompressing an image

Decompress an image using the -d option:

astcenc -d example.astc example.tga

This decompresses example.astc storing the decompressed output to example.tga.

Measuring image quality

Review the compression quality using the -t option:

astcenc -t example.png example.tga

This is equivalent to compressing and then immediately decompressing the image, allowing a visual inspection of the decompression quality. In addition this mode also prints out the PSNR quality of the compressed image to the console.

Experimenting

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 -veryfast, 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.

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 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 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.

tterrace/astc-encoder