Both Panasonic ZS1 and Canon ELPH 520 HS have 10.0 MP resolution sensors but Panasonic ZS1's sensor is 1/2.5-inch (5.744 x 4.308 mm ) and Canon ELPH 520 HS's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Canon ELPH 520 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 ZS1.
Below you can see the ZS1 and ELPH 520 HS sensor size comparison.
As seen above, Canon ELPH 520 HS has a 1.1x Larger sensor area than Panasonic ZS1. 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.