Leica M9-P has a
18.0MP Full frame (36 x 24 mm ) sized CCD sensor . On the other hand, Nikon P510 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Expeed C2 processor.
Another difference between these two cameras is that Leica M9-P's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the M9-P and P510 sensor size comparison.
As seen above, Leica M9-P has a 30.8x Larger sensor area than Nikon P510. 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.