compressedtex.adoc

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 1. Mapping of Vulkan BC formats to descriptions

elink:VkFormat	Khronos Data Format Specification description
Formats described in the “S3TC Compressed Texture Image Formats” chapter
ename:VK_FORMAT_BC1_RGB_UNORM_BLOCK	BC1 with no alpha
ename:VK_FORMAT_BC1_RGB_SRGB_BLOCK	BC1 with no alpha, sRGB-encoded
ename:VK_FORMAT_BC1_RGBA_UNORM_BLOCK	BC1 with alpha
ename:VK_FORMAT_BC1_RGBA_SRGB_BLOCK	BC1 with alpha, sRGB-encoded
ename:VK_FORMAT_BC2_UNORM_BLOCK	BC2
ename:VK_FORMAT_BC2_SRGB_BLOCK	BC2, sRGB-encoded
ename:VK_FORMAT_BC3_UNORM_BLOCK	BC3
ename:VK_FORMAT_BC3_SRGB_BLOCK	BC3, sRGB-encoded
Formats described in the “RGTC Compressed Texture Image Formats” chapter
ename:VK_FORMAT_BC4_UNORM_BLOCK	BC4 unsigned
ename:VK_FORMAT_BC4_SNORM_BLOCK	BC4 signed
ename:VK_FORMAT_BC5_UNORM_BLOCK	BC5 unsigned
ename:VK_FORMAT_BC5_SNORM_BLOCK	BC5 signed
Formats described in the “BPTC Compressed Texture Image Formats” chapter
ename:VK_FORMAT_BC6H_UFLOAT_BLOCK	BC6H (unsigned version)
ename:VK_FORMAT_BC6H_SFLOAT_BLOCK	BC6H (signed version)
ename:VK_FORMAT_BC7_UNORM_BLOCK	BC7
ename: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 2. Mapping of Vulkan ETC formats to descriptions

elink:VkFormat	Khronos Data Format Specification description
ename:VK_FORMAT_ETC2_R8G8B8_UNORM_BLOCK	RGB ETC2
ename:VK_FORMAT_ETC2_R8G8B8_SRGB_BLOCK	RGB ETC2 with sRGB encoding
ename:VK_FORMAT_ETC2_R8G8B8A1_UNORM_BLOCK	RGB ETC2 with punch-through alpha
ename:VK_FORMAT_ETC2_R8G8B8A1_SRGB_BLOCK	RGB ETC2 with punch-through alpha and sRGB
ename:VK_FORMAT_ETC2_R8G8B8A8_UNORM_BLOCK	RGBA ETC2
ename:VK_FORMAT_ETC2_R8G8B8A8_SRGB_BLOCK	RGBA ETC2 with sRGB encoding
ename:VK_FORMAT_EAC_R11_UNORM_BLOCK	Unsigned R11 EAC
ename:VK_FORMAT_EAC_R11_SNORM_BLOCK	Signed R11 EAC
ename:VK_FORMAT_EAC_R11G11_UNORM_BLOCK	Unsigned RG11 EAC
ename: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 3. Mapping of Vulkan ASTC formats to descriptions

elink:VkFormat	Compressed texel block dimensions	Requested mode
ename:VK_FORMAT_ASTC_4x4_UNORM_BLOCK	4 {times} 4	Linear LDR
ename:VK_FORMAT_ASTC_4x4_SRGB_BLOCK	4 {times} 4	sRGB
ename:VK_FORMAT_ASTC_5x4_UNORM_BLOCK	5 {times} 4	Linear LDR
ename:VK_FORMAT_ASTC_5x4_SRGB_BLOCK	5 {times} 4	sRGB
ename:VK_FORMAT_ASTC_5x5_UNORM_BLOCK	5 {times} 5	Linear LDR
ename:VK_FORMAT_ASTC_5x5_SRGB_BLOCK	5 {times} 5	sRGB
ename:VK_FORMAT_ASTC_6x5_UNORM_BLOCK	6 {times} 5	Linear LDR
ename:VK_FORMAT_ASTC_6x5_SRGB_BLOCK	6 {times} 5	sRGB
ename:VK_FORMAT_ASTC_6x6_UNORM_BLOCK	6 {times} 6	Linear LDR
ename:VK_FORMAT_ASTC_6x6_SRGB_BLOCK	6 {times} 6	sRGB
ename:VK_FORMAT_ASTC_8x5_UNORM_BLOCK	8 {times} 5	Linear LDR
ename:VK_FORMAT_ASTC_8x5_SRGB_BLOCK	8 {times} 5	sRGB
ename:VK_FORMAT_ASTC_8x6_UNORM_BLOCK	8 {times} 6	Linear LDR
ename:VK_FORMAT_ASTC_8x6_SRGB_BLOCK	8 {times} 6	sRGB
ename:VK_FORMAT_ASTC_8x8_UNORM_BLOCK	8 {times} 8	Linear LDR
ename:VK_FORMAT_ASTC_8x8_SRGB_BLOCK	8 {times} 8	sRGB
ename:VK_FORMAT_ASTC_10x5_UNORM_BLOCK	10 {times} 5	Linear LDR
ename:VK_FORMAT_ASTC_10x5_SRGB_BLOCK	10 {times} 5	sRGB
ename:VK_FORMAT_ASTC_10x6_UNORM_BLOCK	10 {times} 6	Linear LDR
ename:VK_FORMAT_ASTC_10x6_SRGB_BLOCK	10 {times} 6	sRGB
ename:VK_FORMAT_ASTC_10x8_UNORM_BLOCK	10 {times} 8	Linear LDR
ename:VK_FORMAT_ASTC_10x8_SRGB_BLOCK	10 {times} 8	sRGB
ename:VK_FORMAT_ASTC_10x10_UNORM_BLOCK	10 {times} 10	Linear LDR
ename:VK_FORMAT_ASTC_10x10_SRGB_BLOCK	10 {times} 10	sRGB
ename:VK_FORMAT_ASTC_12x10_UNORM_BLOCK	12 {times} 10	Linear LDR
ename:VK_FORMAT_ASTC_12x10_SRGB_BLOCK	12 {times} 10	sRGB
ename:VK_FORMAT_ASTC_12x12_UNORM_BLOCK	12 {times} 12	Linear LDR
ename:VK_FORMAT_ASTC_12x12_SRGB_BLOCK	12 {times} 12	sRGB

ASTC textures containing any HDR blocks should: not be passed into the API using an sRGB or UNORM texture format.

Note	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.

The ASTC decode mode is decode_float16.

Note that an implementation may: use HDR mode when linear LDR mode is requested.