Olympus E-M10 IV has a
20.0MP Four Thirds (17.4 x 13 mm ) sized CMOS sensor and features TruePic VIII processor. On the other hand, Leica Digilux 3 has a
7.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor .
Olympus E-M10 IV's sensor provides 13MP more than Leica Digilux 3'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-M10 IV and Digilux 3 sensor size comparison.
Olympus E-M10 IV and Leica Digilux 3 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.