Both the camera features same sensor size, but canon features more bright lens and standard ISO range, see the detailed specification comparison review below
Sensor: Both the camera features same sensor, but Canon G15 features better standard ISO range for better low light performance.
Auto Focus: Nikon wins here, Nikon have 99 AF points and Canon have only 9.
Lens: Canon features more bright lens with F1.8-F2.8 aperture range, Nikon have 2X more optical zoom compared to Canon.
Shutter: Nikon have better Long-Exposure mode
Canon have better Top Continuous Shooting Speed
Canon G15 have optical viewfinder, Nikon P7700 missing it.
Video: Nikon offers more frame rate and canon have 24fps format.
Display: Nikon wins: Nikon have articulated display unit but canon have fixed.
See High ISO noise image comparison of Canon G15 vs Nikon P7700
Conclusion: Canon G15 features bit better range High ISO core specification. We recommend you to buy Nikon P7700.
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