Both Canon SX510 HS and Panasonic ZS50 have 12.0 MP resolution sensors but Canon SX510 HS's sensor is 1/2.3-inch (6.17 x 4.55 mm ) and Panasonic ZS50's sensor is (1/2. ).
Since Canon SX510 HS'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 ZS50.
Below you can see the SX510 HS and ZS50 sensor size comparison.
As seen above, Canon SX510 HS has a infx Larger sensor area than Panasonic ZS50. 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.