Panasonic GH4 has a
16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features Venus Engine IX processor. On the other hand, Panasonic G9 has a
20.0MP Four Thirds (17.3 x 13 mm ) sized Live MOS sensor .
One other difference between these two cameras that is worth mentioning is that Panasonic G9's sensor doesn't have an 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 GH4 and G9 sensor size comparison.
Sensor Size and Resolution Comparison image of Panasonic GH4 and Panasonic G9 Cameras
Panasonic GH4 and Panasonic G9 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 Panasonic GH4 has 26% larger pixel area compared to Panasonic G9, 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
Panasonic GH4
or the
Panasonic G9 ,
including hyperfocal distance.
