Olympus VG-120 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, Pentax WG-3 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor .
Below you can see the VG-120 and WG-3 sensor size comparison.
Olympus VG-120 and Pentax WG-3 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 VG-120 has 15% larger pixel area compared to Pentax WG-3, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.