Android developers must meet the strict guidelines when designing icons for their mobile apps. Icon Design Guidelines for Dialog Icons specify icon resolutions and provide guidelines for choosing the color palette and visual styling of images used in pop-up dialogs and interactive prompts.
The Android OS can run on a wide range of hardware platforms equipped with screens of different pixel densities. To accommodate the wide range of displays used in the various devices running the Android OS, the guidelines specify three separate icon sizes for low-, mid- and high-definition displays. These resolutions are specified as 24×24 pixels for low-resolution displays (ldpi), 32×32 pixels for medium-resolution displays (mdpi), and 48×48 pixels for high-definition screens (hdpi).
Style wise, Android dialog icons are flat, face-on images designed with the use of a light gradient and inner shadow. These visual features allow dialog icons to stand out against a dark background. No
isometric or 3D style is allowed in order to maintain a uniform look across Android-compatible apps developed by different vendors.
1. Dialog icons have a 1 pixel safeframe
2. Inner shadow: black, 25% opacity, angle -90°,
distance 1px, size 0px
3. Front part: gradient overlay, angle 90°
bottom: r 223 ; g 223 ; b 223,
top: r 249 ; g 249 ; b 249,
bottom color location: 0%,
top color location: 75%
The Design Guidelines specify exact colors for icon’s overlay. The gradient overlay is laid out at an angle of 90 degrees. The gradient starts from the bottom as 233, 233, 233 (an R,G,B color), and goes up to 249, 249, 249 (R,G,B) at 75% to the top. The space from that point up is filled with a single color of 249, 249, 249 (R,G,B).
The inner shadow is rendered black at 25% opacity (controlled via the alpha-channel) at -90 degrees. The distance from the main picture is 1px, while the size of the shadow is 0px (meaning that the shadow is the size of the main shape itself).
Creating Android-style dialog icons is a fairly easy, step-by-step process. You can create your icons in a graphic editor such as Adobe Photoshop by downloading the Icon Templates Pack for Android 2.3 from the Android Web site. However, a raster editor may not be the perfect way, as you will end up drawing each of the three icon resolutions separately.
To save time producing the three resolutions (ldpi, mdpi and hdpi), a vector tool is advised. You can draw the basic shape of the icon in your favorite vector editor such as Adobe Illustrator and export the shape into Adobe Photoshop, rendering the vector source into the required reaolution (24×24, 32×32, or 48×48 pixels). The rest is simple: add an overlay gradient in a separate layer, and specify the appropriate inner shadow in yet another layer. Save the image as a PSD file for future editing, and export it as a PNG file with transparency enabled to add your newly created icon into your Android app.
To save time designing icons for your Android app, you may choose a ready-made collection instead. The collection of Android Dialog Icons by Aha-Soft http://www.aha-soft.com/stock-icons/android-dialog-icons.htm provides 86 different icons designed in strict accordance with the Dialog Icons Design Guidelines. This royalty-free collection is supplied in the form of PNG files with alpha-channel, and offers PSD source images. In addition, scalable AI and SVG vector sources are available. You can view and purchase the set at the company’s Web site.