Mipmap drawables for icons
There are two distinct uses of mipmaps:
For launcher icons when building density specific APKs. Some developers build separate APKs for every density, to keep the APK size down. However some launchers (shipped with some devices, or available on the Play Store) use larger icon sizes than the standard 48dp. Launchers use getDrawableForDensity and scale down if needed, rather than up, so the icons are high quality. For example on an hdpi tablet the launcher might load the xhdpi icon. By placing your launcher icon in the mipmap-xhdpi directory, it will not be stripped the way a drawable-xhdpi directory is when building an APK for hdpi devices. If you're building a single APK for all devices, then this doesn't really matter as the launcher can access the drawable resources for the desired density.
The actual mipmap API from 4.3. I haven't used this and am not familiar with it. It's not used by the Android Open Source Project launchers and I'm not aware of any other launcher using.
It seems Google have updated their docs since all these answers, so hopefully this will help someone else in future :) Just came across this question myself, while creating a new (new new) project.
TL;DR: drawables may be stripped out as part of dp-specific resource optimisation. Mipmaps will not be stripped.
Different home screen launcher apps on different devices show app launcher icons at various resolutions. When app resource optimization techniques remove resources for unused screen densities, launcher icons can wind up looking fuzzy because the launcher app has to upscale a lower-resolution icon for display. To avoid these display issues, apps should use the
mipmap/resource folders for launcher icons. The Android system preserves these resources regardless of density stripping, and ensures that launcher apps can pick icons with the best resolution for display.
(from http://developer.android.com/tools/projects/index.html#mipmap)
How are these mipmap images different from the other familiar drawable images?
Here is my two cents in trying to explain the difference. There are two cases you deal with when working with images in Android:
You want to load an image for your device density and you are going to use it "as is", without changing its actual size. In this case you should work with drawables and Android will give you the best fitting image.
You want to load an image for your device density, but this image is going to be scaled up or down. For instance this is needed when you want to show a bigger launcher icon, or you have an animation, which increases image's size. In such cases, to ensure best image quality, you should put your image into mipmap folder. What Android will do is, it will try to pick up the image from a higher density bucket instead of scaling it up. This will increase sharpness (quality) of the image.
Thus, the rule of thumb to decide where to put your image into would be:
- Launcher icons always go into mipmap folder.
- Images, which are often scaled up (or extremely scaled down) and whose quality is critical for the app, go into mipmap folder as well.
- All other images are usual drawables.