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    Appendix C: 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.

    Table 91. Mapping of Vulkan BC formats to descriptions
    VkFormat Khronos Data Format Specification description

    Formats described in the “S3TC Compressed Texture Image Formats” chapter

    VK_FORMAT_BC1_RGB_UNORM_BLOCK

    BC1 with no alpha

    VK_FORMAT_BC1_RGB_SRGB_BLOCK

    BC1 with no alpha, sRGB-encoded

    VK_FORMAT_BC1_RGBA_UNORM_BLOCK

    BC1 with alpha

    VK_FORMAT_BC1_RGBA_SRGB_BLOCK

    BC1 with alpha, sRGB-encoded

    VK_FORMAT_BC2_UNORM_BLOCK

    BC2

    VK_FORMAT_BC2_SRGB_BLOCK

    BC2, sRGB-encoded

    VK_FORMAT_BC3_UNORM_BLOCK

    BC3

    VK_FORMAT_BC3_SRGB_BLOCK

    BC3, sRGB-encoded

    Formats described in the “RGTC Compressed Texture Image Formats” chapter

    VK_FORMAT_BC4_UNORM_BLOCK

    BC4 unsigned

    VK_FORMAT_BC4_SNORM_BLOCK

    BC4 signed

    VK_FORMAT_BC5_UNORM_BLOCK

    BC5 unsigned

    VK_FORMAT_BC5_SNORM_BLOCK

    BC5 signed

    Formats described in the “BPTC Compressed Texture Image Formats” chapter

    VK_FORMAT_BC6H_UFLOAT_BLOCK

    BC6H (unsigned version)

    VK_FORMAT_BC6H_SFLOAT_BLOCK

    BC6H (signed version)

    VK_FORMAT_BC7_UNORM_BLOCK

    BC7

    VK_FORMAT_BC7_SRGB_BLOCK

    BC7, sRGB-encoded

    ETC Compressed Image Formats

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

    Table 92. Mapping of Vulkan ETC formats to descriptions
    VkFormat Khronos Data Format Specification description

    VK_FORMAT_ETC2_R8G8B8_UNORM_BLOCK

    RGB ETC2

    VK_FORMAT_ETC2_R8G8B8_SRGB_BLOCK

    RGB ETC2 with sRGB encoding

    VK_FORMAT_ETC2_R8G8B8A1_UNORM_BLOCK

    RGB ETC2 with punch-through alpha

    VK_FORMAT_ETC2_R8G8B8A1_SRGB_BLOCK

    RGB ETC2 with punch-through alpha and sRGB

    VK_FORMAT_ETC2_R8G8B8A8_UNORM_BLOCK

    RGBA ETC2

    VK_FORMAT_ETC2_R8G8B8A8_SRGB_BLOCK

    RGBA ETC2 with sRGB encoding

    VK_FORMAT_EAC_R11_UNORM_BLOCK

    Unsigned R11 EAC

    VK_FORMAT_EAC_R11_SNORM_BLOCK

    Signed R11 EAC

    VK_FORMAT_EAC_R11G11_UNORM_BLOCK

    Unsigned RG11 EAC

    VK_FORMAT_EAC_R11G11_SNORM_BLOCK

    Signed RG11 EAC

    ASTC Compressed Image Formats

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

    Table 93. Mapping of Vulkan ASTC formats to descriptions
    VkFormat Compressed texel block dimensions Requested mode

    VK_FORMAT_ASTC_4x4_UNORM_BLOCK

    4 × 4

    Linear LDR

    VK_FORMAT_ASTC_4x4_SRGB_BLOCK

    4 × 4

    sRGB

    VK_FORMAT_ASTC_5x4_UNORM_BLOCK

    5 × 4

    Linear LDR

    VK_FORMAT_ASTC_5x4_SRGB_BLOCK

    5 × 4

    sRGB

    VK_FORMAT_ASTC_5x5_UNORM_BLOCK

    5 × 5

    Linear LDR

    VK_FORMAT_ASTC_5x5_SRGB_BLOCK

    5 × 5

    sRGB

    VK_FORMAT_ASTC_6x5_UNORM_BLOCK

    6 × 5

    Linear LDR

    VK_FORMAT_ASTC_6x5_SRGB_BLOCK

    6 × 5

    sRGB

    VK_FORMAT_ASTC_6x6_UNORM_BLOCK

    6 × 6

    Linear LDR

    VK_FORMAT_ASTC_6x6_SRGB_BLOCK

    6 × 6

    sRGB

    VK_FORMAT_ASTC_8x5_UNORM_BLOCK

    8 × 5

    Linear LDR

    VK_FORMAT_ASTC_8x5_SRGB_BLOCK

    8 × 5

    sRGB

    VK_FORMAT_ASTC_8x6_UNORM_BLOCK

    8 × 6

    Linear LDR

    VK_FORMAT_ASTC_8x6_SRGB_BLOCK

    8 × 6

    sRGB

    VK_FORMAT_ASTC_8x8_UNORM_BLOCK

    8 × 8

    Linear LDR

    VK_FORMAT_ASTC_8x8_SRGB_BLOCK

    8 × 8

    sRGB

    VK_FORMAT_ASTC_10x5_UNORM_BLOCK

    10 × 5

    Linear LDR

    VK_FORMAT_ASTC_10x5_SRGB_BLOCK

    10 × 5

    sRGB

    VK_FORMAT_ASTC_10x6_UNORM_BLOCK

    10 × 6

    Linear LDR

    VK_FORMAT_ASTC_10x6_SRGB_BLOCK

    10 × 6

    sRGB

    VK_FORMAT_ASTC_10x8_UNORM_BLOCK

    10 × 8

    Linear LDR

    VK_FORMAT_ASTC_10x8_SRGB_BLOCK

    10 × 8

    sRGB

    VK_FORMAT_ASTC_10x10_UNORM_BLOCK

    10 × 10

    Linear LDR

    VK_FORMAT_ASTC_10x10_SRGB_BLOCK

    10 × 10

    sRGB

    VK_FORMAT_ASTC_12x10_UNORM_BLOCK

    12 × 10

    Linear LDR

    VK_FORMAT_ASTC_12x10_SRGB_BLOCK

    12 × 10

    sRGB

    VK_FORMAT_ASTC_12x12_UNORM_BLOCK

    12 × 12

    Linear LDR

    VK_FORMAT_ASTC_12x12_SRGB_BLOCK

    12 × 12

    sRGB

    VK_FORMAT_ASTC_4x4_SFLOAT_BLOCK

    4 × 4

    HDR

    VK_FORMAT_ASTC_5x4_SFLOAT_BLOCK

    5 × 4

    HDR

    VK_FORMAT_ASTC_5x5_SFLOAT_BLOCK

    5 × 5

    HDR

    VK_FORMAT_ASTC_6x5_SFLOAT_BLOCK

    6 × 5

    HDR

    VK_FORMAT_ASTC_6x6_SFLOAT_BLOCK

    6 × 6

    HDR

    VK_FORMAT_ASTC_8x5_SFLOAT_BLOCK

    8 × 5

    HDR

    VK_FORMAT_ASTC_8x6_SFLOAT_BLOCK

    8 × 6

    HDR

    VK_FORMAT_ASTC_8x8_SFLOAT_BLOCK

    8 × 8

    HDR

    VK_FORMAT_ASTC_10x5_SFLOAT_BLOCK

    10 × 5

    HDR

    VK_FORMAT_ASTC_10x6_SFLOAT_BLOCK

    10 × 6

    HDR

    VK_FORMAT_ASTC_10x8_SFLOAT_BLOCK

    10 × 8

    HDR

    VK_FORMAT_ASTC_10x10_SFLOAT_BLOCK

    10 × 10

    HDR

    VK_FORMAT_ASTC_12x10_SFLOAT_BLOCK

    12 × 10

    HDR

    VK_FORMAT_ASTC_12x12_SFLOAT_BLOCK

    12 × 12

    HDR

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

    Note

    An HDR block in a texture passed using a LDR UNORM format will return the appropriate ASTC error color if the implementation supports only the ASTC LDR profile, but may result in either the error color or a decompressed HDR color if the implementation supports HDR decoding.

    ASTC decode mode

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

    Table 94. Mapping of Vulkan ASTC decoding format to ASTC decoding modes
    VkFormat Decoding mode

    VK_FORMAT_R16G16B16A16_SFLOAT

    decode_float16

    VK_FORMAT_R8G8B8A8_UNORM

    decode_unorm8

    VK_FORMAT_E5B9G9R9_UFLOAT_PACK32

    decode_rgb9e5

    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.

    Table 95. Mapping of Vulkan PVRTC formats to descriptions
    VkFormat Compressed texel block dimensions sRGB-encoded

    VK_FORMAT_PVRTC1_2BPP_UNORM_BLOCK_IMG

    8 × 4

    No

    VK_FORMAT_PVRTC1_4BPP_UNORM_BLOCK_IMG

    4 × 4

    No

    VK_FORMAT_PVRTC2_2BPP_UNORM_BLOCK_IMG

    8 × 4

    No

    VK_FORMAT_PVRTC2_4BPP_UNORM_BLOCK_IMG

    4 × 4

    No

    VK_FORMAT_PVRTC1_2BPP_SRGB_BLOCK_IMG

    8 × 4

    Yes

    VK_FORMAT_PVRTC1_4BPP_SRGB_BLOCK_IMG

    4 × 4

    Yes

    VK_FORMAT_PVRTC2_2BPP_SRGB_BLOCK_IMG

    8 × 4

    Yes

    VK_FORMAT_PVRTC2_4BPP_SRGB_BLOCK_IMG

    4 × 4

    Yes