ASTCformat

ASTCformat refers to the Adaptive Scalable Texture Compression (ASTC) scheme, a texture compression format designed to reduce memory footprint and bandwidth for real-time rendering while preserving image quality. Developed under the Khronos Group with contributions from Arm and other industry partners, ASTC was introduced to unify and improve upon prior mobile and desktop texture formats by offering flexible compression options and broad hardware support.

Technical overview: ASTC compresses 2D and, in capable implementations, 3D textures in fixed-size blocks. A single texture can be encoded using a range of block dimensions, typically from 4x4 up to 12x12 texels for 2D textures, with 3D variants available for volumetric textures. All blocks are encoded in a uniform 128-bit container, enabling a wide spectrum of bitrates and quality levels. The format supports both linear and sRGB color spaces, and can handle various channel configurations, including luminance and alpha, depending on the block mode. This design allows developers to tailor the balance between image fidelity and memory usage for different content and hardware.

Encoding and decoding: ASTC utilizes per-block color endpoints and index patterns to reconstruct texels during sampling. Encoders such as the official astcenc tool from Arm, along with other software libraries, produce ASTC-compressed textures. Decoding is performed by GPU hardware or software decoders within graphics drivers, enabling efficient sampling directly in shaders.

Adoption and use: ASTC has broad hardware and API support, including modern GPUs and graphics APIs such as Vulkan and OpenGL ES. It is widely used in mobile applications, games, and content pipelines for its ability to deliver high visual quality at low to moderate bitrates, with a versatile range of block sizes that suits diverse textures and platforms.

File formats and containers: ASTC textures are typically stored with the .astc extension and are commonly packaged in containers like KTX2 for use in modern engines and tooling.