I am guessing it is the way it is saved. A smaller resolution for internet. I don't think it shoots at 4 and 8, just saves it. However, the D7200 and a few others are capable of switching from the standard DX size to an additional 1.3x crop which reduces the size of the sensor capturing the image. It will give you a little boost in frames per second. A small box appears in the viewfinder letting you know the area of capture.
