Casio EX-Z450 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor . 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 EX-Z450 and SP-620 UZ sensor size comparison.
Casio EX-Z450 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 Casio EX-Z450 has 32% 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.