All attempts so far to produce a DXT1 with no alpha (0x83f0), have only resulted in a DXT1A with 1-bit alpha (0x83f1). The result is the same even when the source .png has had all alpha data stripped completely from it.
It's not clear what the DXT1UseAlpha option does.
$ magick atlas.png -background white -alpha remove -alpha off PNG24:atlas_rgb.png
$ compressonatorcli -fd DXT1 -DXT1UseAlpha 0 atlas_rgb.png atlas_dxt1.ktx
/usr/lib/compressonator-cli-bin/compressonatorcli
Processing source : atlas_rgb.png
Processing destination: atlas_dxt1.ktx
Source data size = 16777216 Bytes, width = 2048 px height = 2048 px
Destination data size = 2097152 Bytes Resulting compression ratio = 8.00:1
Done Processing
$ ktxinfo atlas_dxt1.ktx Header
identifier: «KTX 11»\r\n\x1A\n
endianness: 0x4030201
glType: 0
glTypeSize: 1
glFormat: 0
glInternalformat: 0x83f1
glBaseInternalformat: 0x1908
pixelWidth: 2048
pixelHeight: 2048
pixelDepth: 0
numberOfArrayElements: 0
numberOfFaces: 1
numberOfMipLevels: 1
bytesOfKeyValueData: 0
No Key/Value data.
Data Sizes (bytes)
------------------
Level 0: 2097152
Total: 2097152
All attempts so far to produce a DXT1 with no alpha (0x83f0), have only resulted in a DXT1A with 1-bit alpha (0x83f1). The result is the same even when the source .png has had all alpha data stripped completely from it.
It's not clear what the
DXT1UseAlphaoption does.