Panasonic G100 has a
20.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor . On the other hand, Nikon S1200pj has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor .
Panasonic G100's sensor provides 6MP more than Nikon S1200pj's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the G100 and S1200pj sensor size comparison.
As seen above, Panasonic G100 has a 8.0x Larger sensor area than Nikon S1200pj. 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.