Image quality in shared photostream

Hello,

I started to use iCloud photo library which works fine and I have all the photos in iCloud in original quality (at least at seems like so to me).

But when I start a shared photostream and put the photos there and I open it on my Mac in new app Photo, what quality do have these images?

The reason I am asking it is because I take many pictures and chosen one I store to shared photostream. And time from time I would like to save them to my HDD and store them in original quality.

Thank you for clearing this question.