The last High Sierra and Catalina can’t install 2019.1 or .2. The installer is 32-bit only. Somehow existing PVRTexToolCLI runs, so it must be a 64-bit app, but the installer prevents getting the newest version.
Some questions on PVRTexTool…
With -f ASTC_4x4,UBN,sRGB, the colors are converted from the png data (already sRGB), to sRGB space which is incorrect. This setting should only affect the format. The only current workaround is to us lRGB, and then change the format in the KTX header. I’d reported this 2 years back.
It’s nice to finally see BC1-3 support back on macOS. BC4/5_unorm/snorm (rgtc) are just the 1x or 2x the alpha chunk that you already have in BC3, so would be nice to see those added. Also need BC1-3_SRGB. And eventually BC6H/BC7 (bptc).
Also make sure the -p (premultiply setting) is performed while in linear color space, and then apply sRGB. Otherwise, overflow occurs. Also the same when building mips - these are done in premultiplied linear values, and then sRGB applied. I haven’t tried the premutiplied setting, but would like to.