Androi Supporting Multiple Screens

ldpi (low) ~120dpi 0.75
mdpi (medium) ~160dpi
1
hdpi (high) ~240dpi
1.5
xhdpi (extra-high) ~320dpi 2
xxhdpi (extra-extra-high) ~480dpi
3
xxxhdpi (extra-extra-extra-high) ~640dpi 4

Note: You only need to provide density-specific drawables for bitmap files (

.png

,

.jpg

, or

.gif

)
and Nine-Patch files (

.9.png

). If you use XML files to define shapes, colors, or other drawable
resources, you should put one copy in the default drawable directory (

drawable/

).

To create alternative bitmap drawables for different densities, you should follow the 3:4:6:8:12:16 scaling ratio between the six generalized densities. For example, if you have a bitmap drawable that's 48x48 pixels for medium-density screens,
all the different sizes should be:

36x36 (0.75x) for low-density
48x48 (1.0x baseline) for medium-density
72x72 (1.5x) for high-density
96x96 (2.0x) for extra-high-density
180x180 (3.0x) for extra-extra-high-density
192x192 (4.0x) for extra-extra-extra-high-density (launcher icon only; see note above)

当我们把一个图片资源放入其中一个drawble-xx的文件夹中时，

那么，加载到内存中的图片尺寸 = 实际尺寸*当前dpi/图片所在的Dpi

比如

手机dpi = 240（对应目录hdpi）

图片的实际宽和高 分别为 1600,1200

以宽度举例

将图片放入drawable-mdpi目录里加到内存后是 2400*1800
1600*1.5/1

将图片放入drawable-hdpi目录里加到内存后是 1600*1200 1600*1.5/1.5
将图片放入drawable-xhdpi目录里加到内存后是1200*900

1600*1.5/2
将图片放入drawable-xxhdpi目录里加到内存后是800*600
1600*1.5/3

将图片放入drawable目录里加到内存后是
1600*1200
1600

将图片放入drawable-nodpi目录里加到内存后是1600*1200
1600

图片放在drawable中，等同于放在drawable-mdpi中，原因为：drawable目录不具有屏幕密度特性，所以采用基准值，即mdpi

参考：本地文档 file:///F:/AndroidSDK/docs/guide/practices/screens_support.html