android xdpi folders, what size for my image?

Question

I've been reading the following: http://developer.android.com/guide/practices/screens_support.html

It's about the folders res-long-land-hdpi, res-notlong-land-dpi, res-notlong-port-ldpi etc. And what they actually mean and when they should be used.

The article also says the following:

xlarge screens are at least 960dp x 720dp
large screens are at least 640dp x 480dp

I'm developing for a device that is: 1280 x 720 and one that is 480 x 800

My app will only be available in portrait mode.

So that means i have to put images in the res-long-port-hdpi folder for the first device, and in res-notlong-port-ldpi for the second device right?

Then the next problem i have with this is. I have an image which is 332 x 226 pixels. This looks fine on the first (xlarge) device. But to what size do i have to rescale this image so that i can place it in the (lower resolution) res-xx-xx-ldpi folder?

I'm not sure how to calculate the new sizes for the different folders.

Ted Hopp · Accepted Answer · 2012-08-03 18:22:03Z

8

The size ratios should match the nominal pixel densities as Android defines them:

ldpi - 120 pixels/inch; dpi scale = .75 (4 dpi = 3 pixels)
mdpi - 160 pixels/inch; dpi scale = 1 (1 dpi = 1 pixel)
hdpi - 240 pixels/inch; dpi scale = 1.5 (2 dpi = 3 pixels)
xhdpi - 320 pixels/inch; dpi scale = 2 (1 dpi = 2 pixels)

So if you make your xhdpi images twice the size (in pixels) of the mdpi resources, they will be the same dpi, meaning they will be the same physical size on their respective screens.

edited Aug 3, 2012 at 18:22

answered Aug 3, 2012 at 18:15

Ted Hopp

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2 Comments

w00 Over a year ago

So does this mean that if i use an image for an xhdpi screen 400 x 300 (is the image size) then the size for an mdpi should be 200 x 150. And for an hdpi it's 300 x 225. Is that what you're saying?

Ted Hopp Over a year ago

@w00 - Exactly (assuming you are measuring image size in pixels). This will result in the image being the same physical size (in inches) on different devices, regardless of pixel density of the devices. (This isn't exact, because device pixel densities don't always exactly match Android's four density categories. For instance, a device with pixel density of 170 pixels/inch will be treated by the system as mdpi. In that case, the images will be slightly smaller in inches than nominal.)

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