Casio EX-S12 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor . On the other hand, Ricoh WG-4 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor .
Below you can see the EX-S12 and WG-4 sensor size comparison.
Casio EX-S12 and Ricoh WG-4 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-S12 has 32% larger pixel area compared to Ricoh WG-4, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.