Leica Q2 Monochrom has a
47.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Maestro II processor. On the other hand, Ricoh GR III has a
24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor .
Leica Q2 Monochrom's sensor provides 23MP more than Ricoh GR III'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 similarity between these two cameras is that both Ricoh GR III and Leica Q2 Monochrom sensors lack anti-alias (Low-Pass) filters. 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 Q2 Monochrom and GR III sensor size comparison.
As seen above, Leica Q2 Monochrom has a 2.4x Larger sensor area than Ricoh GR III. 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.