.KTX2 File Format

Introduction

KTX 2 is the second version of the Khronos Group’s texture container, built around Vulkan. The texture format is a Vulkan VkFormat number, and a Khronos data format descriptor spells out the exact layout of every texel, so a reader does not need a table of graphics API constants.

Each mipmap level can be supercompressed on its own: with Zstandard or zlib for any format, or with BasisLZ for Basis Universal ETC1S data, which a loader transcodes to whatever block-compressed format the graphics card supports. This makes KTX 2 the texture format of the glTF extension KHR_texture_basisu. Its media type is image/ktx2.

Structure

The file is little-endian throughout. A fixed 80-byte header and index are followed by the level index, then the data format descriptor, the key and value data, any supercompression global data, and the mipmap levels, smallest first. The reference pages cover the header and level layout, the data format descriptor, the key and value data and supercompression.

Variants

• Khronos Texture 1 – OpenGL textures described by OpenGL constants, in either byte order
• Khronos Texture 2 – Vulkan textures with a data format descriptor and optional supercompression

Links