Canon SX20 IS has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Digic 4 processor. On the other hand, Panasonic GH3 has a
16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features Venus Engine VII FHD processor.
Below you can see the SX20 IS and GH3 sensor size comparison.
As seen above, Panasonic GH3 has a 8.0x Larger sensor area than Canon SX20 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.