I can't find specific specifications on the Full versus Medium resolution, so I ran a quick test. Those are the only two resolution settings.
At the default Full resolution, I took a picture and it showed 12.5MP resolution (3072 x 4080), consuming 2.4MB of storage.
I changed to Medium resolution and shot the same scene. It resulted in a picture of 4.9MP (1920 x 2560) and 1.1 MB storage.
Note that the normal image is a 4:3 aspect ratio. You can also select a cropped 16:9 aspect ratio which will reduce the image sizes even more. the Full resolution image becomes 9.1 MP (2268 x 4032) 2.1 MB and Medium resolution becomes 4.1MP (1512 x 2688) and 0.99MP
Hope that helped.