Canon SX120 IS has a
10.0MP 1/2.5-inch (5.744 x 4.308 mm ) sized CCD sensor and features Digic 4 processor. On the other hand, Canon ELPH 100 HS has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features DIGIC 4 with iSAPS technology processor.
Below you can see the SX120 IS and ELPH 100 HS sensor size comparison.
As seen above, Canon ELPH 100 HS has a 1.1x Larger sensor area than Canon SX120 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.