I want to keep an image in the res/drawable folder, which would be used as the background in my app. I wish that my app should work across all devices of varying densities. What minimum size in pixels should the image be kept to maintain balance between a reasonable app size and also supporting multiple screens.

The developer guide mentions that:

```
xlarge screens are at least 960dp x 720dp
large screens are at least 640dp x 480dp
normal screens are at least 470dp x 320dp
small screens are at least 426dp x 320dp

```

I use Photoshop where the images are always in pixels and not dp and hence the confusion. By the way, I am quite new at Android as well as Photoshop.