Both Panasonic G9 and Panasonic GX8 have Four Thirds sized 20.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Another difference between these two cameras is that Panasonic G9'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 G9 and GX8 sensor size comparison.
Sensor Size and Resolution Comparison image of Panasonic G9 and Panasonic GX8 Cameras
Panasonic G9 and Panasonic GX8 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Panasonic G9
or the
Panasonic GX8 ,
including hyperfocal distance.
