When designing mobile apps or designing graphics for Android apps, one must follow srict guidelines. Re-using images made for other operating systems, especially desktop-based, is generally not a good idea. Foreign graphics will look out of place at best, or will make your Android apps hardly recognizable at worst.
There exist precise guidelines available for designing standard-compliant Android icons. Different design guidelines are available for tab icons and menu graphics.
Tab icons are drawn in individual tabs in tabbed UI. Tab icons should be provided in two different states: selected and unselected. It is required that tab icons are drawn as simple, flat shapes as opposed to icons drawn in 3D or isometric projection.
Android OS and Android apps are used on a variety of different platforms employing a wide range of hardware. In connection to icon images, those platforms can have different display sizes, display resolutions, pixel dimensions and density. To accommodate the wide range of screens, Android developers must supply all tab icons used in their apps in at least three resolutions to be shown on low, medium, and high density displays. Resolution-wise, the outer boundaries for the three resolutions are defined as 24×24, 32×32, and 48×48 pixels. Inner dimensions should not exceed 22×22, 28×28, and 42×42 pixels respectively. By providing all three standard resolutions, developers can ensure that their apps will be shown properly on a wide range of platforms running the Android OS.
Menu icons are used in the “options” menu, and are displayed to the user when they press the Menu button. Similar to tab icons, menu icons should be flat, grayscale images. Just as tab icons, developers cannot use 3D or isometric projections.
Pixel sizes for menu icons are described in a slightly more complex way as opposed to to tab icons. Instead of two resolutions defined for tab graphics (inner shape and boundary box), the inner shape of menu icons can be smaller or bigger depending on whether they are square-shaped or not. If a menu icon is square-shaped, its dimensions should be smaller than for icons with different shapes. The reason for having two different size limits is to establish a consistent visual weight across the two icon types.
The outer dimensions for ldpi, mdpi and hdpi icons are described as 36×36, 48×48, and 72×72 pixels respectively. Inner shapes for square, low-definition icons is 22×22 pixels, while non-square icons should fit into a boundary box sized 24×24 dots. Similarly, mdpi icons should fit 30×30 and 32×32 pixel boxes, while high-definition images should fit into 44×44 and 48×48 pixel rectangles respectively.
Instead of designing your own graphics conforming to these guidelines, Android developers have an option of getting stock icons from professional designers. For example, Android Tab Icons by Aha-Soft offer 112 unique tab images in selected and unselected states and all standard sizes. Should additional resolutions be required, developers can produce graphics at any size by accessing scalable vector sources. Android Tab Icons can be previewed and downloaded at http://www.aha-soft.com/stock-icons/android-tab-icons.htm.