In order to create custom icons and assign them to applications, you'll need to know what kind of software can simplify the job for you, the design limitations you'll need to consider, and how to assign the icon to an application.
At first blush, designing icons for a software application or touch screen may seem very much like creating their counterparts for a Web page. In both cases, the visual symbols you create need to communicate important concepts in a very limited space and to a potentially diverse, international audience. However, you'll encounter more stringent design standards and conventions for creating custom Windows or Mac desktop icon files (from angling a shadow correctly to indicating transparency in a BMP file) than you'll run across for most Web graphics creation.
In this article, we'll examine:
What limitations you'll face or design considerations to bear in mind when creating icons for the Windows or Macintosh desktop.
How to leverage transparent bitmap drawing functions to knock out an icon's background color process that differs from creating a transparent GIF for a Web page.
What file formats you'll work with when saving images for use as icons.
Let's take just a moment first to consider your icons' purpose. As graphical user interfaces for computers and instruments like touch screens have come into mainstream use, icons typically replace or enhance word labels that direct users to perform functions.
The functions that icons typically represent include activities like choosing tools, launching or navigating within a window or Web page, activating menus, pointing to an onscreen item, revealing the state of a set of data, and implementing changes.
Icons can stand for data, files, directories, disks, or provide a means by which to manipulate them, such as open or delete icons. You'd do well to use well-known concepts for example, an image of a clock face for a timed-activity or timer icon wherever possible to ensure your icons' meanings are as clear as possible to your audience.
Sizing Up Your Icons
You'll have the greatest flexibility if you design full-color, 24-bit icons in the largest sizes required. Under Mac OS X, icons can measure up to 128 x 128 pixels, while the largest size for Windows XP icons is 48 x 48 pixels. You can then reduce and clean up or create a simpler version of each icon to display well at the smaller standard icon sizes (such as 32 x 32 or 16 x 16 pixels), and when reduced to an 8-bit color (or 256-color) palette.
When you save a Windows icon graphic in the standard .ico file format for icons, for example, you can embed up to nine images to accommodate three sizes at three different bit depths. The valid image sizes are 48 x 48, 32 x 32, and 16 x 16 pixels; the three-color depths are 4-bit, 8-bit, and 24-bit color.
Creating icons for your taskbar or system tray usually calls for another specific set of parameters. Under Windows, such icons measure 16 x 16 pixels; under Mac OS X, taskbar icons measure 32 x 32 pixels.
Icon editing applications are specifically designed to facilitate creating different versions of your icons at various sizes and color depths (see Figure 1). You'll learn more about the capabilities of icon editors in the second part of this article.
Figure 1 Use an icon editor to create or open an icon file containing images that vary by size or color depth.
Under Mac OS X, any icon that displays in the Finder such as application icons or document icons can be magnified in the Dock or previewed at full size (see Figure 2). In addition, users can specify a preferred size for viewing icons. So, at a minimum you'll need to provide what's known as a thumbnail icon, a full-size baseline image measuring 128 x 128 pixels.
Figure 2 In Mac OS X, icons can display at sizes ranging from 16 x 16 pixels to 128 x 128 pixels.
The Mac OS can scale down this size when necessary like when a user sets the Dock to a smaller size but extremely detailed icons won't display well when scaled down from thumbnails. To avoid scaling problems with your icons, you should also provide smaller versions of each icon measuring 64 x 64, 32 x 32, and 16 x 16 pixels.
Both Microsoft and Apple provide detailed guidelines for designing icons for their respective operating systems.
With the advent of Windows XP, Microsoft's Windows User Experience Team released Creating Windows XP Icons, an extremely comprehensive set of guidelines that walks users through conceptualizing icons, creating 24-bit graphics, reducing to 8-bit and even 4-bit color, and the range of Windows icon sizes.
Apple's website for developers devotes a chapter in its human-computer interface guidelines to Icons.