Olympus E-PL2 has a
12.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features Truepic V processor. On the other hand, YI M1 has a
20.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor .
YI M1's sensor provides 8MP more than Olympus E-PL2'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.
Below you can see the E-PL2 and M1 sensor size comparison.
Sensor Size and Resolution Comparison image of Olympus E-PL2 and YI M1 Cameras
Olympus E-PL2 and YI M1 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. On the other hand, since Olympus E-PL2 has 65% larger pixel area compared to YI M1, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.
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-PL2
or the
YI M1 ,
including hyperfocal distance.