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, Canon SX30 IS has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Digic 4 processor.
Below you can see the SX20 IS and SX30 IS sensor size comparison.
Canon SX20 IS and Canon SX30 IS have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.