Sigma fp L has a
61.0MP Full frame (36 x 24 mm ) sized BSI-CMOS sensor . On the other hand, Panasonic FP3 has a
14.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor and features Venus Engine IV processor.
Sigma fp L's sensor provides 47MP more than Panasonic FP3'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 fp L and FP3 sensor size comparison.
As seen above, Sigma fp L has a 31.2x Larger sensor area than Panasonic FP3. 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.