extraction of ASTC HDR 6x6: fatal message from ktx tool

[richgel999]

I'm not sure if this is noted elsewhere in the Issues. If I try to extract a standard ASTC HDR 6x6 .KTX2 file to .EXR with ktx, I get this fatal message:

C:\dev\ktx2_2\KTX-Software-main\build\Debug>ktx extract c:\dev\bu_2_13\basis_universal\bin\astc_hdr_6x6\Desk.ktx2 1.exr
ktx extract fatal: Requested format conversion from VK_FORMAT_ASTC_6x6_SFLOAT_BLOCK is not supported.

Note extracting UASTC HDR 4x4 and UASTC HDR 6x6i (with or without mipmaps) to .EXR now works fine. From a user value perspective, basisu supports strong RDO encoding to ASTC HDR 6x6, and this format is a faster to transcode alternative vs. UASTC HDR 6x6i (because it's just standard ASTC HDR, so on ASTC devices there is no transcode step at all, just fast Zstd decompression).

We've updated our "KTX2 File Format Support Technical Details" wiki page with the latest info for our users:

KTX2 File Format Support Technical Details

[MarkCallow]

Is ASTC HDR 6x6 support new in Basis Universal 2.x?

If we want to fix this in the upcoming release, the simplest way is to fix ktxTexture2_DecodeAstc to support the HDR formats. The underlying decoder supports them.

[richgel999]

Is ASTC HDR 6x6 support new in Basis Universal 2.x?

v1.6 (the version you're already using) supports RDO ASTC HDR 6x6 compression, and it works pretty well. It's one of the first RDO ASTC encoders (either LDR or HDR) available to the public. Internally it's the same compressor as UASTC HDR 6x6i, except it outputs standard ASTC HDR 6x6 texture data. It takes the same codec configuration parameters (i.e. the same "lambda" value to control rate vs. distortion) you're already using. We didn't make any changes to it for v2.0.

[MarkCallow]

Please provide a sample ASTC HDR 6x6 file for testing.

Do you recommend extracting to 16- or 32-bit float?

[MarkCallow]

Can you apply RDO to UASTC HDR 4x4? If so, what parameter do you use?

[richgel999]

Can you apply RDO to UASTC HDR 4x4? If so, what parameter do you use?

The current encoder doesn't support RDO UASTC HDR 4x4. It's possible, but it's not been a priority yet. (The UASTC HDR 4x4 and ASTC HDR 6x6/UASTC HDR 6x6i encoders share the same low level ASTC HDR helper code, but differ at the higher levels.)

[richgel999]

Please provide a sample ASTC HDR 6x6 file for testing.
Do you recommend extracting to 16- or 32-bit float?

UASTC/ASTC HDR decodes to FP16, so anything beyond that is likely a waste.

KTX2 file attached ("Desk.ktx2"). It validates with ktx.exe:

C:\dev\ktx2_2\KTX-Software-main\build\Debug>ktx info C:\dev\bu_2_13\basis_universal\bin\astc_hdr_6x6\Desk.ktx2
Validation successful

Header

identifier: «KTX 20»\r\n\x1A\n
vkFormat: VK_FORMAT_ASTC_6x6_SFLOAT_BLOCK
typeSize: 1
pixelWidth: 644
pixelHeight: 874
pixelDepth: 0
layerCount: 0
faceCount: 1
levelCount: 1
supercompressionScheme: KTX_SS_ZSTD
dataFormatDescriptor.byteOffset: 0x68
dataFormatDescriptor.byteLength: 44
keyValueData.byteOffset: 0x94
keyValueData.byteLength: 60
supercompressionGlobalData.byteOffset: 0
supercompressionGlobalData.byteLength: 0

Level Index

Level0.byteOffset: 0xd0
Level0.byteLength: 243833
Level0.uncompressedByteLength: 252288

Data Format Descriptor

DFD total bytes: 44
Vendor ID: KHR_DF_VENDORID_KHRONOS
Descriptor type: KHR_DF_KHR_DESCRIPTORTYPE_BASICFORMAT
Version: KHR_DF_VERSIONNUMBER_1_3
Descriptor block size: 40
Flags: 0x0 (KHR_DF_FLAG_ALPHA_STRAIGHT)
Transfer: KHR_DF_TRANSFER_LINEAR
Primaries: KHR_DF_PRIMARIES_BT709
Model: KHR_DF_MODEL_ASTC
Dimensions: 6, 6, 1, 1
Plane bytes: 16, 0, 0, 0, 0, 0, 0, 0
Sample 0:
    Qualifiers: 0xC0 (KHR_DF_SAMPLE_DATATYPE_SIGNED, KHR_DF_SAMPLE_DATATYPE_FLOAT)
    Channel Type: 0x0 (KHR_DF_CHANNEL_ASTC_DATA)
    Length: 128 bits Offset: 0
    Position: 0, 0, 0, 0
    Lower: 0xbf800000
    Upper: 0x3f800000

Key/Value Data

KTXmapRange:
    scale: 1.000000
    offset: 0.000000
KTXwriter: Basis Universal 2.10

Desk.zip