Dual pixel technology is for autofocusing in camera. Samsung galaxy S7 uses this technology in its camera for providing autofocus. The prior models like Samsung galaxy S6, galaxy S5 and Apple iPhone 6 use phase-detection autofocus(PDAF).
In PDAF usually, ~5% – 10% of total pixels are equipped with focusing photodiodes and these are called focus pixels. Whereas in Galaxy S7 all the pixels are equipped with focusing photodiodes this will result in better focusing speed and in focus result even for rapidly moving objects.
More focus pixels is the reason camera’s megapixels in Galaxy S7 are less than Galaxy S6. S7 have a 12MP camera whereas its predecessor S6 have a 16MP camera. The number of focusing pixels are increased so to keep cost in limits total number pixels are decreased, but this is not hampering image quality for 2 reasons. First we already discussed a better focusing system that will ensure crisp images every time and second is larger pixel size that will enable the camera to capture more light.
With dual pixel technology, Galaxy s7 is able to provide feature likes Motion panorama.
video source:samsung newsroom.