Android drawables DPI

Question

I have an Android app with 4 versions of the same image, in each of these folders:

drawable-ldpi/
drawable-mdpi/
drawable-hdpi/
drawable-xhdpi/

The only difference between the images is the size, I simply took the original large image and scaled it down according to the formula:

120dp lpdi, 1 dp=0.75 px
160dp mpdi, 1 dp=1 px
240dp hdpi, 1 dp=1.5 px
320dp xhpdi, 1 dp=2 px

The problem is I intend to have over 100 images, so to reduce the file size can't I just put the xhdpi versions in the drawables/ folder instead of having 4 versions of each image, then Android can scale the image as required? What is the disadvantage of doing it this way? Is it simply a trade off between performance and file size?

Answer 1

You can just put the xhdpi versions in the drawable resources. Then in your layout/xml files specify the images dimensions in dp. Android will downscale your images accordingly. As long as you are downscaling the drawable resources quality of the image wont change.

Answer 2

You can. The disadvantage may be slightly worse image quality: consider for hdpi display you need to scale 240/320 times, that is, 0.75, or to speak e.g. in 1D pixel line you make up 3 target pixels out of 4 source pixels. Most of the time it will look very good, but I imagine some pixel art may be an exception. I guess this may be slower as well, and use more memory than it could, but I didn't measure that so I can't tell for sure.

P.S. I'm using this method (providing xhdpi resources only) myself too.

Answer 3

having only the xhdpi resource will degrade A LOT your app performance. Plus on low-range devices (small screens and small memory) it's very likely that the VM will run out of memory and crash whilst processing those large bitmaps.

You can develop everything on your high end device and use a simple photoshop automation to create the other resources but it's better to have a bigger APK than your app not working on mid and low range devices.

Another option might be to export several APK (one for each screen type) and use the manifest to specify which screen sizes it does support and let the market filter the right APK to the right device.