4:8 would mean one number is double the other; for every 4 pixels in one direction, there are 8 pixels in the other direction. This is not the case, since 5760 is clearly much more than double 1200. 1920x1200 is 16:10, so three of those side by side would have triple the width, but the same height. Therefore, 48:10, or 24:5.
8/16/14 at 4:47pm