Both Panasonic ZS7 and Ricoh GXR GR Lens A12 28mm F2.5 have 12.0 MP resolution sensors but Panasonic ZS7's sensor is 1/2.3-inch (6.08 x 4.56 mm ) and Ricoh GXR GR Lens A12 28mm F2.5's sensor is APS-C (23.6 x 15.7 mm ).
Since Ricoh GXR GR Lens A12 28mm F2.5'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 ZS7.
Below you can see the ZS7 and GXR GR Lens A12 28mm F2.5 sensor size comparison.
As seen above, Ricoh GXR GR Lens A12 28mm F2.5 has a 13.4x Larger sensor area than Panasonic ZS7. 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.