Olympus E-P7 has a
20.0MP Four Thirds (17.4 x 13 mm ) sized CMOS sensor and features TruePic VIII processor. On the other hand, Panasonic GF1 has a
12.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features Venus Engine HD processor.
Olympus E-P7's sensor provides 8MP more than Panasonic GF1's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Another difference between these two cameras is that Olympus E-P7's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the E-P7 and GF1 sensor size comparison.
Sensor Size and Resolution Comparison image of Olympus E-P7 and Panasonic GF1 Cameras
Olympus E-P7 and Panasonic GF1 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Olympus E-P7
or the
Panasonic GF1 ,
including hyperfocal distance.