The Android app icon should be an Alpha channel transparent 32-bit PNG image. Due to the large number of Android devices, an application icon needs to be designed in several different sizes, such as:
LDPI (Low Density screen,120 DPI) with an icon size of X-px.
MDPI (Medium Density screen, DPI) with an icon size of x px.
HDPI (High Density-screen, + DPI) with an icon size of X-px.
XHDPI (extra-high density screen, at + DPI), with an icon size of X-px.
It is recommended that in the design process, a few pixels are vacated around the perimeter so that the design icon is visually consistent with the other icons, for example,
The X-px icon allows the drawing area to be set to a size of X-px, with 4 pixels around it for filling (no background).
The X-px icon allows the paint area to be set to a size of 2 pixels, which is used for filling (no background).
The X PX icon allows the drawing area to be set to a total of 1 pixels (without background) for the size of the range x px.
The X-px icon allows the drawing area to be set to the X-px and 1 pixels around it for filling (no background).
Http://tech.sina.com.cn/s/2010-11-03/09514822757_2.shtml
Http://wenku.baidu.com/link?url=kjrR22tvV8cd5f3LX_ Wou8ge3nafngojpwizbcrsvgln2bteanh2os7dsh0prf3zgzlwt9xo5fwo7jcri7d6iwdmpurtat-dctmgpeukfck