Creating Android background, how many pixels?

Question

I want to create backgrounds for my Android game. And while reading here I get how it works, what I don't get is how to set the correct size in Photoshop for the different folders.

Here is the list from Android Developers:

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

But what would this be in pixels? Since Photoshop doesn't have dp. How can I make a list like the following?

• Small screens are at least <Insert pixel size here>
• Normal screens are at least <Insert pixel size here> (...)

I don't want my background to stretch and shrink to much, so I would like at least four different sizes.

Answer 1

One of the key things on the Supporting Multiple Screens page you linked is this:

To create alternative bitmap drawables for different densities, you should follow the 3:4:6:8 scaling ratio between the four generalized densities. For example, if you have a bitmap drawable that's 48x48 pixels for medium-density screen (the size for a launcher icon), all the different sizes should be:

36x36 for low-density 48x48 for medium-density 72x72 for high-density 96x96 for extra high-density

That being said, since we know most of the screen sizes and densities available (here's a neat reference page I just found: http://blog.blundell-apps.com/list-of-android-devices-with-pixel-density-buckets/), you can use that as a guide, too. So, to create a background which fills screen, I would focus on width resolution. Most popular phones are either 320, 480, 540 or 720 pixels in width. So I would create my backgrounds as such (phones only... you can do the math for tablets)
mdpi: 320 wide
hdpi: 540 wide
hxdpi: 720 wide

Height is a bit more complicated because not all phones are the same aspect ratio. Depending on your app you have the option of scaling height or clipping height.

I'd also take a look at the Screen Sizes and Densities chart on this page: http://developer.android.com/about/dashboards/index.html. As you can see ldpi is a tiny percentage, so you might prefer to just let android do the scaling. On the other hand, ldpi images are likely small in file size, so if you want to make sure it looks great, you can provide the assets. For xlarge tablets you probably only care about mdpi right now.