Canon G1 X III has a
24.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features DIGIC 7 processor. On the other hand, Sigma DP2 Quattro has a
20.0MP APS-C (23.5 x 15.7 mm ) sized CMOS (Foveon X3) sensor and features TRUE III engine processor.
Below you can see the G1 X III and DP2 Quattro sensor size comparison.
Sensor Size and Resolution Comparison image of Canon G1 X III and Sigma DP2 Quattro Cameras
As seen above, Sigma DP2 Quattro has a 1.1x Larger sensor area than Canon G1 X III. 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.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Canon G1 X III
or the
Sigma DP2 Quattro ,
including hyperfocal distance.