Nikon P7100 has a 10.0MP 1/1.7" (7.44 x 5.58 mm ) sized CCD sensor and features Expeed C2 processor. On the other hand, Nikon P7700 has a 12.0MP 1/1.7" (7.44 x 5.58 mm ) sized CMOS sensor .
Below you can see the P7100 and P7700 sensor size comparison.
Nikon P7100 and Nikon P7700 have 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 Nikon P7100 has 20% larger pixel area compared to Nikon P7700, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.
DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. It 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. Nikon P7100 and Nikon P7700 sensors have been tested by DxO and the results show that P7700 has a better overall score of 53, 12 points higher compared to P7100's score of 41.