In Eclipse there are different folders for each size (xxhdpi, xhdpi, hdpi…)
They are there in Android Studio too. The Android Tools team kinda hid them.
If you look just above the project explorer tree thingy on the left, you should see a drop-down, one that probably says “Android” right now:
That is the Android project view, one that gives you a somewhat synthetic look at your project, collapsing things like resource sets and sourcesets to hide those details.
Eclipse users will probably be happier with the classic project view, which you get by clicking that drop-down and switching it to “Project”:
This works much like Eclipse’s Package Explorer, where you get an actual filesystem view of what’s going on, complete with resource set directories.
It’s all the same stuff on the filesystem, but the Android project view masks it a bit.
Right click drawable ->
Image Asset ->
Asset Type: Action Bar and Tab Icons.
Image file: image_path,
Resource Name: how_youre_image_will_be_called ->
This will add 4 different sizes of your image so that it will fit depending the device size (phone, tablet…)
You can also
ctrl+v to drawable folder and pick the size you want (mdpi – phones, xxhdpi – tablets…) but it would not resize by devices type