Nikon P300 has a 12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Expeed C2 processor. On the other hand, Olympus SZ-30MR has a 16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CMOS sensor and features TruePic III+ processor.
Below you can see the P300 and SZ-30MR sensor size comparison.
Nikon P300 and Olympus SZ-30MR have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Nikon P300 has 32% larger pixel area compared to Olympus SZ-30MR, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.