Canon 400D has a 10.0MP APS-C
(22.2 x 14.8 mm ) sized CMOS sensor . On the other hand, Panasonic FZ70 has a 16.0MP 1/2.3-inch
(6.17 x 4.55 mm ) sized CMOS sensor and features Venus Engine processor.
Panasonic FZ70's sensor provides 6MP more than Canon 400D'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 400D and FZ70 sensor size comparison.
As seen above, Canon 400D has a 11.7x Larger sensor area than Panasonic FZ70. 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.
DxOMark Sensor Scores
Both Canon 400D and Panasonic FZ70 sensors have been tested by DxoMark. DxoMark scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Of the two cameras that we are comparing, 400D has scored 62, 21 points higher than FZ70.