Optimal settings

Hi, I’ve recently started looking into KTX2.0 and would love some feedback about optimal settings. I’m converting 3 different textures for my project, Albedo, Normal and a packed texture which includes AO, roughness and metallic. The file size output I’m getting seems high to me, for the packed texture compared to .astc compression.

Here is what I’m using to convert my image files (PNG):
Albedo: toktx -bcmp -qlevel 255 -clevel 5 --lower_left_maps_to_s0t0
Normal: toktx --assign_oetf linear -normalmap --uastc 15 --uastc_rdo_l [.25,.75] --zcmp 15 --lower_left_maps_to_s0t0
Packed texture: toktx --assign_oetf linear --uastc 15 --uastc_rdo_l [.25,10] --zcmp 15 --lower_left_maps_to_s0t0

My results:

TestImage01.png 1024 x 1024

PNG: 1.03 mb
KTX2: 743 kb
ASTC: 257 kb

TestImage02.png 2048 x 2048

PNG: 2.18 mb
KTX2: 1.82 mb
ASTC: 1.025

How can I optimise these settings while retaining visual quality?

Thank you for your time.

What is the difference between your KTX2 and ASTC versions? KTX2 is a file format that can store images in a number of different formats, including any of the ASTC compressed formats. So what image format are you using in the KTX2 version that’s different from the ASTC version?

Also, which ASTC formats are you using? How many channels are in each image?