- RGB_11_11_10 is exported in a RGBA PNG file where the 4 channels are
used as a uint32 storing a RGB_10_11_11_REV pixel.
We use the .rgb32f extension, and those PNG files contain garbage
when seen in a PNG viewer.
- This is now the default for the -x option.
- compressed KTX files don't encode RGBM, which means they can't
support HDR, unless an HDR compression scheme is used.