Ricoh CX1 has a
9.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CMOS sensor and features Smooth Imaging Engine IV processor. On the other hand, Ricoh GR Digital III has a
10.0MP 1/1.7-inch (7.44 x 5.58 mm ) sized CCD sensor and features GR engine III processor.
Below you can see the CX1 and GR Digital III sensor size comparison.
As seen above, Ricoh GR Digital III has a 1.5x Larger sensor area than Ricoh CX1. 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.