Panasonic S1 II has a
24.0MP Full frame (35.6 x 23.8 mm ) sized Partially-Stacked CMOS sensor and features Venus Engine processor. On the other hand, Leica M-Monochrom has a
18.0MP Full frame (36 x 24 mm ) sized Monochrome CCD sensor .
Panasonic S1 II's sensor provides 6MP more than Leica M-Monochrom'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 Panasonic S1 II'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 S1 II and M-Monochrom sensor size comparison.
Sensor Size and Resolution Comparison image of Panasonic S1 II and Leica M-Monochrom Cameras
Panasonic S1 II and Leica M-Monochrom 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
Panasonic S1 II
or the
Leica M-Monochrom ,
including hyperfocal distance.