How to correctly read the jpg images of optical flow?

I'm trying to use optical flow images of the JHMDB dataset from here.
The optical flow type it provided is Brox flow and the format is jpg image (one sample)
But, for my understanding, the optical flow should be 2-channel, representing x and y component.
So, my question is how to convert a jpg image into a 2-channel optical flow or what's the correct way to read such optical flow images?