Ricoh GR III has a
24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor . On the other hand, Canon G9 X II has a
20.0MP 1″ (13.2 x 8.8 mm ) sized BSI-CMOS sensor and features DIGIC 7 processor.
Another difference between these two cameras is that Ricoh GR III's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the GR III and G9 X II sensor size comparison.
As seen above, Ricoh GR III has a 3.2x Larger sensor area than Canon G9 X II. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.