I've got an interesting conundrum...
We recently upgraded from 10.0 to 10.3.1 and my issue has only been happening since the udpate.
When I'm in Data View, my aerial imagery source is super clear, it's very tight resolution imagery.
When I'm in Layout View, the aerial imagery deterioroates and pixellates BIG time.
It doesn't matter if I export it as PDF, PNG, JPG, WITH or without image compression (I've tried all the different settings), it just keeps giving me grainy images...
perhaps calculate statistics for the local image.... according to this thread
I did a keyword search on geonet using .... imagery quality export ... limited to 1 year, there are other hits