Panasonic FZ100 has a
14.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CMOS sensor and features Venus Engine FHD processor. On the other hand, Panasonic ZS99 has a
20.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Venus Engine processor.
Panasonic ZS99's sensor provides 6MP more than Panasonic FZ100'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 FZ100 and ZS99 sensor size comparison.
Sensor Size and Resolution Comparison image of Panasonic FZ100 and Panasonic ZS99 Cameras
Panasonic FZ100 and Panasonic ZS99 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 FZ100
or the
Panasonic ZS99 ,
including hyperfocal distance.