Both Panasonic S5 and Canon G1 X III have 24.0 MP resolution sensors but Panasonic S5's sensor is Full frame (35.6 x 23.8 mm ) and Canon G1 X III's sensor is APS-C (22.3 x 14.9 mm ).
Since Panasonic S5's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Canon G1 X III.
Another difference between these two cameras is that Panasonic S5'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 moire occurring in certain scenes.
Below you can see the S5 and G1 X III sensor size comparison.
As seen above, Panasonic S5 has a 2.5x Larger sensor area than Canon G1 X III. 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.