ASTC Evaluation Codec

For more information on ASTC, take a look at the ARM Multimedia Blog posts "ASTC Texture Compression: ARM Pushes the Envelope in Graphics Technology" and "ARM Unveils Details of ASTC Texture Compression at HPG Conference".

I have started this thread for users of this evaluation tool to ask questions. Here's a very quick "getting started" guide:

First, accept the license, download the tarball and unpack. In the subdirectories Win32, Mac OS X and Linux32 are binaries for, you guessed it, Windows, Mac OS X, and Linux (x86 versions). If you are running on another system, you might like to try compiling from source - take a look at Source/buildinstructions.txt .

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 a very extensive help message, including usage instructions, and details of all the possible options.

First, find a 24-bit .png or .tga file you wish to use, say /images/example.png (or on windows C:\images\example.png).

You can compress it using the -c option, like this (use the first line for Linux or Mac OS, second line for Windows users):

./astcenc -c /images/example.png /images/example-compressed.astc 6x6 -medium
astcenc -c C:\images\example.png C:\images\example-compressed.astc 6x6 -medium

The -c indicates a compression operation, followed by the input and output filenames. The block footprint size follows, in this case 6x6 pixels, then the requested compression speed, medium.

To decompress the file again, you should use:

astcenc -d /images/example-compressed.astc /images/example-decompressed.tga
astcenc -d C:\images\example-compressed.astc C:\images\example-decompressed.tga

The -d indicates decompression, followed by the input and output filenames. The output file will be an uncompressed TGA image.

If you just want to test what compression and decompression are like, use the test mode:

astcenc -t /images/example.png /images/example-decompressed.tga 6x6 -medium
astcenc -c C:\images\example.png C:\images\example-compressed.tga 6x6 -medium

This is equivalent to compressing and then immediately decompressing again, and it also prints out statistics about the fidelity of the resulting image, using the peak signal-to-noise ratio.

Take a look at the input and output images.

The block footprints go from 4x4 (8 bits per pixel) all the way up to 12x12 (0.89 bits/pixel). Like any lossy codec, such as JPEG there will come a point where selecting too aggressive a compression results in inacceptable quality loss, and ASTC is no exception. Finding this optimum balance between size and quality is one place where ASTC excels since its compression ratio is adjustable in much finer steps than other texture codecs.

The compression speed runs 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.

So, download, run, have a play, and post any questions or results on this thread.