Olympus SP-810 UZ has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features TruePic III+ processor. On the other hand, Olympus SP-620 UZ has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features TruePic III+ processor.
Below you can see the SP-810 UZ and SP-620 UZ sensor size comparison.
Olympus SP-810 UZ and Olympus SP-620 UZ have the same 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 Olympus SP-810 UZ has 15% larger pixel area compared to Olympus SP-620 UZ, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.