Nikon P900 has a 16.0MP 1/2.3" (6.17 x 4.55 mm ) sized CMOS sensor and features Expeed C2 processor. On the other hand, Olympus 1s has a 12.0MP 1/1.7" (7.44 x 5.58 mm ) sized BSI-CMOS sensor .
Below you can see the P900 and 1s sensor size comparison.
As seen above, Olympus 1s has a 1.5x Larger sensor area than Nikon P900. 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.