Ricoh WG-4 GPS has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor . On the other hand, Sony T90 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor .
Below you can see the WG-4 GPS and T90 sensor size comparison.
Ricoh WG-4 GPS and Sony T90 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 Sony T90 has 32% larger pixel area (2.34µm2 vs 1.76µm2) compared to Ricoh WG-4 GPS, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.