Sony A58 has a 20.0MP APS-C (23.2 x 15.4 m ) sized CMOS sensor . On the other hand, Panasonic S5 II has a 24.0MP Full frame (35.6 x 23.8 mm ) sized CMOS sensor and features Venus Engine processor.
One other difference between these two cameras that is worth mentioning is that Panasonic S5 II's sensor doesn't have an 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 A58 and S5 Mark II sensor size comparison.
As seen above, Panasonic S5 II has a 2.4x Larger sensor area than Sony A58. 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.