General
Icons are small images, which can be associated to file types, executables, to
identify and recognize them easier. Double clicking an icon opens / executes the
file.
Structure
An icon contains more images in different size and format. Each image can
contain a transparent area. Windows chooses the file format needed from the icon.
If the icon does not contain the given format, Windows chooses an appropriate
one and resize it. This can result in image loss. The file format is chosen based on
the screen settings, and the size is chosen like follows:
· 16x16: Displayed on the task bar, lists and headers
· 32x32: Displayed on the desktop, control panel
· 48x48: Displayed in Explorer when thumbnail or titles view is selected
· 256x256: Windows Vista® only
Image Formats
Image formats recommended for icons:
The 256x256 formats are needed only for Windows Vista.
Windows XP icons
With the introduction of XP the icon format changed, a new image format was
placed inside the icon, a 32 bit image. This image format contains transparency
information also known as alpha channel, or opacity. This allows that the
background image can blend through the icon. With the help of this feature we
can create shadow effects, semi transparent icons and more.
Windows Vista icons
With Windows Vista another standard icon size was introduced 256x256. This
would result in big icons, so images with the size 256x256 can be compressed
using PNG compression, resulting in smaller file size..
