Fujifilm S1 has a 16.0MP 1/2.3" (6.17 x 4.55 mm ) sized CMOS sensor . On the other hand, Panasonic FZ2500 has a 20.0MP 1" (13.2 x 8.8 mm ) sized BSI-CMOS sensor and features Venus Engine processor.
Below you can see the S1 and FZ2500 sensor size comparison.
As seen above, Panasonic FZ2500 has a 4.1x Larger sensor area than Fujifilm S1. 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.