Compressed Image Formats

The compressed texture formats used by Vulkan are described in the specifically identified sections of the Khronos Data Format Specification, version 1.3.

Unless otherwise described, the quantities encoded in these compressed formats are treated as normalized, unsigned values.

Those formats listed as sRGB-encoded have in-memory representations of R, G and B components which are nonlinearly-encoded as R', G', and B'; any alpha component is unchanged. As part of filtering, the nonlinear R', G', and B' values are converted to linear R, G, and B components; any alpha component is unchanged. The conversion between linear and nonlinear encoding is performed as described in the KHR_DF_TRANSFER_SRGB section of the Khronos Data Format Specification.

Block-Compressed Image Formats

BC1, BC2, and BC3 formats are described in S3TC Compressed Texture Image Formats chapter of the Khronos Data Format Specification. BC4 and BC5 are described in the RGTC Compressed Texture Image Formats chapter. BC6H and BC7 are described in the BPTC Compressed Texture Image Formats chapter.

ETC Compressed Image Formats

The following formats are described in the ETC2 Compressed Texture Image Formats chapter of the Khronos Data Format Specification.

ASTC Compressed Image Formats

ASTC formats are described in the ASTC Compressed Texture Image Formats chapter of the Khronos Data Format Specification.

ASTC textures containing HDR block encodings should be passed to the API using an ASTC SFLOAT texture format.

ASTC Decode Mode

If the VK_EXT_astc_decode_mode extension is enabled, the decode mode is determined as follows:

Otherwise, the ASTC decode mode is decode_float16.

Note that an implementation may use HDR mode when linear LDR mode is requested unless the decode mode is decode_unorm8.

PVRTC Compressed Image Formats

PVRTC formats are described in the PVRTC Compressed Texture Image Formats chapter of the Khronos Data Format Specification.