GoPro Hero9 Black has a
23.0MP (1/2. ) sized CMOS sensor and features GP1 processor. On the other hand, Leica V-Lux 4 has a
12.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CMOS sensor .
GoPro Hero9 Black's sensor provides 11MP more than Leica V-Lux 4'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 Hero9 Black and V-Lux 4 sensor size comparison.
As seen above, Leica V-Lux 4 has a infx Larger sensor area than GoPro Hero9 Black. 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.