So, as most iOS developers know, it a pain in the ass having to get all the images and their dimensions. I am currently using quite a handy tool called Resizer. The app will resize a 2x image to a standard image size, so then you only have to deal with the 2x images, you will be surprised with how much time this has saved me.

https://itunes.apple.com/us/app/resizer/id411277085?mt=12