plumageRender/data/environments/README.md

Additional environment cube maps put here must be

• Stored as Khronos texture format files (.ktx)
• Cube maps (with mip maps)
• 16 bit HDR RGBA signed float (VK_FORMAT_R16G16B16A16_SFLOAT)

Converting hdr environment maps can be done with cmft like this:

cmft --input "papermill.hdr" --filter none --outputNum 1 --output0 "papermill_hdr16f_cube" --output0params ktx,rgba16f,cubemap --generateMipChain true --dstFaceSize 512