Good official lessons teach Caching Bitmaps and Managing Bitmap Memory

When your app have to load a number of bitmap, memory allocation will get complicated. Here is official lessons from developer.android.com.

• Caching Bitmaps teach you using a memory and disk bitmap cache to improve the responsiveness and fluidity of your UI when loading multiple bitmaps.
• Managing Bitmap Memory teach specific things you can do to facilitate garbage collection and bitmap reuse.

Also, the video Bitmap Allocation by DevBytes introduce how to speed up bitmap loading and reduce garbage collection by reusing existing bitmaps.