Nikon S31 has a
10.0MP 1/2.9-inch (4.96 x 3.72 mm ) sized CCD sensor . On the other hand, Casio EX-ZR10 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Exilim Engine HS processor.
Below you can see the S31 and EX-ZR10 sensor size comparison.
As seen above, Casio EX-ZR10 has a 1.5x Larger sensor area than Nikon S31. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.