iCloud Photos, really full resolution?

Hello,

When I try to email a photo from my iPhone, I get asked the usual question of "what size do I want to email it in". In this case, I get the original photo size, 3.8MB. When I download the same photo from my iCloud backup (I have iPhoto backup turned on) the photo that gets downloaded is only 1.7MB in size, and apparently less in resolution.

I thought that my photos were backed up in full resolution on iCloud? I have more than enough space left by the way. Any thoughts?

Thanks in advance,

Sammy