Canon SX1 IS has a
10.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CMOS sensor . On the other hand, Canon G1 X has a
14.0MP 1.5-inch (18.7 x 14 mm ) sized CMOS sensor and features Digic 5 processor.
Below you can see the SX1 IS and G1 X sensor size comparison.
As seen above, Canon G1 X has a 9.3x Larger sensor area than Canon SX1 IS. 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.