Adaptive Scalable Texture Compression

Adaptive Scalable Texture Compression (ASTC) is a lossy block-based texture compression algorithm developed by Jørn Nystad et al. of ARM Ltd. and AMD.

Full details of ASTC were first presented publicly at the High Performance Graphics 2012 conference, in a paper by Olson et al. entitled "Adaptive Scalable Texture Compression"

ASTC was adopted as an official extension for both OpenGL and OpenGL ES by the Khronos Group on 6 August 2012.

Both profiles (LDR and Full) are supported on the latest Mali versions, including the Mali™-T620, Mali-T720, Mali-T760, Mali-T820/T830 and Mali-T860/T880. Nvidia's Kepler and Maxwell-based Tegra.

The method of compression is an evolution of Color Cell Compression with features including numerous closely spaced fractional bit rates, multiple color formats, support for High Dynamic Range (HDR) textures, and real 3D texture support.

The stated primary design goal for ASTC is to enable content developers to have better control over the space/quality tradeoff inherent in any lossy compression scheme. With ASTC, the ratio between adjacent bit rates is of the order of 25%, making it less expensive to increase quality for a given texture.

Encoding different assets often requires different color formats. ASTC allows a wide choice of input formats, including luminance-only, luminance-alpha, RGB, RGBA, and modes optimized for surface normals. The designer can thus choose the optimal format without having to support multiple different compression schemes.

The choices of bit rate and color format do not constrain each other, so that it's possible to choose from a large number of combinations.

Despite this flexibility, ASTC achieves better peak signal-to-noise ratios than PVRTC, S3TC, and ETC2 when measured at 2 and 3.56 bits per texel. For HDR textures, it produces results comparable to BC6H at 8 bits per texel.

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