Both Fujifilm F660EXR and Panasonic ZS45 have 16.0 MP resolution sensors but Fujifilm F660EXR's sensor is 1/2-inch (6.4 x 4.8 mm ) and Panasonic ZS45's sensor is 1/2.33 (6.08 x 4.56 mm ).
Since Fujifilm F660EXR'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 Panasonic ZS45.
Below you can see the F660EXR and ZS45 sensor size comparison.
As seen above, Fujifilm F660EXR has a 1.1x Larger sensor area than Panasonic ZS45. 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.