Panasonic G9 has a
20.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor . On the other hand, Fujifilm HS30EXR has a
16.0MP 1/2-inch (6.4 x 4.8 mm ) sized EXRCMOS sensor and features EXR processor.
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 HS30EXR sensor size comparison.
Sensor Size and Resolution Comparison image of Panasonic G9 and Fujifilm HS30EXR Cameras
As seen above, Panasonic G9 has a 7.3x Larger sensor area than Fujifilm HS30EXR. 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.