For iOS and Android projects we're constantly having to export Photoshop designs to the individual assets. It gets very tedious to use the Slice Tool in Photoshop to manually draw boxes around all the assets you want exported and to hide/show groups to get the right transparency and backgrounds.
Well, if you're still doing it this way I have a recommendation! Slicy which is just plain awesome. It's the best $29 I've ever spent.
Take a look at the "How it works" video on that page, but in a nutshell you name your Groups or Assets in a Photoshop file as Foo@2x.png and Slicy will perfectly slice these from the layers and export both the 2x and 1x image sizes. You still have to make sure that the designs use even pixels, but otherwise it works great. That's it. Done. It can even export automatically every time a change is made to the Photoshop file.
We even use it on Android even though it's originally built for iOS. We will use Foo.png instead of the iOS naming of @2x.png (with the designs made for xxhdpi with a resolution of 1080x1920). We then take the directory we had Slicy to export to and use a our android shell script (droidsize.py) to export these to all the other dpi's.