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 79. 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 80. 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 81. Mapping of Vulkan ASTC formats to descriptions
VkFormat Compressed texel block dimensions sRGB-encoded Profile

VK_FORMAT_ASTC_4x4_UNORM_BLOCK

4 × 4

No

LDR

VK_FORMAT_ASTC_4x4_SRGB_BLOCK

4 × 4

Yes

LDR

VK_FORMAT_ASTC_5x4_UNORM_BLOCK

5 × 4

No

LDR

VK_FORMAT_ASTC_5x4_SRGB_BLOCK

5 × 4

Yes

LDR

VK_FORMAT_ASTC_5x5_UNORM_BLOCK

5 × 5

No

LDR

VK_FORMAT_ASTC_5x5_SRGB_BLOCK

5 × 5

Yes

LDR

VK_FORMAT_ASTC_6x5_UNORM_BLOCK

6 × 5

No

LDR

VK_FORMAT_ASTC_6x5_SRGB_BLOCK

6 × 5

Yes

LDR

VK_FORMAT_ASTC_6x6_UNORM_BLOCK

6 × 6

No

LDR

VK_FORMAT_ASTC_6x6_SRGB_BLOCK

6 × 6

Yes

LDR

VK_FORMAT_ASTC_8x5_UNORM_BLOCK

8 × 5

No

LDR

VK_FORMAT_ASTC_8x5_SRGB_BLOCK

8 × 5

Yes

LDR

VK_FORMAT_ASTC_8x6_UNORM_BLOCK

8 × 6

No

LDR

VK_FORMAT_ASTC_8x6_SRGB_BLOCK

8 × 6

Yes

LDR

VK_FORMAT_ASTC_8x8_UNORM_BLOCK

8 × 8

No

LDR

VK_FORMAT_ASTC_8x8_SRGB_BLOCK

8 × 8

Yes

LDR

VK_FORMAT_ASTC_10x5_UNORM_BLOCK

10 × 5

No

LDR

VK_FORMAT_ASTC_10x5_SRGB_BLOCK

10 × 5

Yes

LDR

VK_FORMAT_ASTC_10x6_UNORM_BLOCK

10 × 6

No

LDR

VK_FORMAT_ASTC_10x6_SRGB_BLOCK

10 × 6

Yes

LDR

VK_FORMAT_ASTC_10x8_UNORM_BLOCK

10 × 8

No

LDR

VK_FORMAT_ASTC_10x8_SRGB_BLOCK

10 × 8

Yes

LDR

VK_FORMAT_ASTC_10x10_UNORM_BLOCK

10 × 10

No

LDR

VK_FORMAT_ASTC_10x10_SRGB_BLOCK

10 × 10

Yes

LDR

VK_FORMAT_ASTC_12x10_UNORM_BLOCK

12 × 10

No

LDR

VK_FORMAT_ASTC_12x10_SRGB_BLOCK

12 × 10

Yes

LDR

VK_FORMAT_ASTC_12x12_UNORM_BLOCK

12 × 12

No

LDR

VK_FORMAT_ASTC_12x12_SRGB_BLOCK

12 × 12

Yes

LDR

VK_FORMAT_ASTC_4x4_SFLOAT_BLOCK_EXT

4 × 4

No

HDR

VK_FORMAT_ASTC_5x4_SFLOAT_BLOCK_EXT

5 × 4

No

HDR

VK_FORMAT_ASTC_5x5_SFLOAT_BLOCK_EXT

5 × 5

No

HDR

VK_FORMAT_ASTC_6x5_SFLOAT_BLOCK_EXT

6 × 5

No

HDR

VK_FORMAT_ASTC_6x6_SFLOAT_BLOCK_EXT

6 × 6

No

HDR

VK_FORMAT_ASTC_8x5_SFLOAT_BLOCK_EXT

8 × 5

No

HDR

VK_FORMAT_ASTC_8x6_SFLOAT_BLOCK_EXT

8 × 6

No

HDR

VK_FORMAT_ASTC_8x8_SFLOAT_BLOCK_EXT

8 × 8

No

HDR

VK_FORMAT_ASTC_10x5_SFLOAT_BLOCK_EXT

10 × 5

No

HDR

VK_FORMAT_ASTC_10x6_SFLOAT_BLOCK_EXT

10 × 6

No

HDR

VK_FORMAT_ASTC_10x8_SFLOAT_BLOCK_EXT

10 × 8

No

HDR

VK_FORMAT_ASTC_10x10_SFLOAT_BLOCK_EXT

10 × 10

No

HDR

VK_FORMAT_ASTC_12x10_SFLOAT_BLOCK_EXT

12 × 10

No

HDR

VK_FORMAT_ASTC_12x12_SFLOAT_BLOCK_EXT

12 × 12

No

HDR

ASTC decode mode

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

Table 82. 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.

PVRTC Compressed Image Formats

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

Table 83. 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