Fujifilm S1 has a 16.0MP 1/2.3" (6.17 x 4.55 mm ) sized CMOS sensor . On the other hand, Panasonic FZ1000 has a 20.0MP 1" (13.2 x 8.8 mm ) sized CMOS sensor and features Venus Engine processor.
Below you can see the S1 and FZ1000 sensor size comparison.
As seen above, Panasonic FZ1000 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.