Panasonic G7 has a
16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor . On the other hand, Panasonic GH1 has a
12.0MP Four Thirds (18.89 x 14.48 mm ) sized CMOS sensor and features Venus Engine HD processor.
Below you can see the G7 and GH1 sensor size comparison.
As seen above, Panasonic GH1 has a 1.2x Larger sensor area than Panasonic G7. 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.