Windows IconsWindows ICO Specification
Windows icons can be more complicated than you might think
As with all the other software platforms that support icons files, Icons for Windows have there very own set of sizes and specifications.
Icons for Windows use a Windows specific file format called ICO. This is an incredibly flexible image ‘container’ that can be used to hold a single image – much like a JPEG or PNG – or it can include many different image sizes and colour depths. When used in a native Windows environment, the correct image is displayed automatically, making the format very user friendly as long as the icon designer has included the necessary sizes and formats for the system you wish to use it in.
If you want to see the different sizes included in the Windows ICO Format you can easily do this in Windows.
Save your ICO files into a folder and then use the ‘View’ drop down to select the view or size of icon you wish to see. Windows 7 automatically scales the icons as you move between the sizes you have created. You can test this by moving the slider up and down.
The actual sizes displayed at each of the headings are as follows:
- Extra Large Icons – 256 x 256 pixels
- Large Icons – 96 x 96 pixels (Automatically rendered by Windows from 256 version)
- Medium Icons – 48 x 48 pixels
- Small Icons – 16 x 16 pixels
- List – 16 x 16 pixels
- Details – 16 x 16 pixels
- Tiles – 48 x 48 pixels
- Content – 32 x 32 pixels
Windows Icon Sizes
To cover all possible uses, the default file sizes needed within an icon for windows are:
- 32bit (24bit colour + 8bit Transparency)
- 8 bit (256 colours + 1 bit transparency)
However there are other relatively common optional sizes that can be included in the Windows ICO Format & utilised by Windows, such as 128×128, 96×96 80×80, 72×72, 64×64 and 24×24 pixels. It is also possible to add any custom sizes you like but generally theses will only be utilised if the software they are created for has the ability to display the custom sizes. This flexibility is great for designers and developers alike but the more and the larger sizes included affects the file size (Kb), so including absolutely every option isn’t generally recommended, especially as there is likely to be a cost associated with having your designer create the extra sizes.
Windows Icon Colours
As each new version of Windows was released, the ability to display more colours has expanded. The Windows Icon ICO format has also expanded to reflect this and maintain backwards compatibility with earlier versions. Because of this, you have the ability to create different colour bit-rate versions of each icon.
Windows 7 and above support 24bit with 8bit transparency, this gives the highest quality image available with a nice graduated transparency, meaning no jagged edges and that most icons can be displayed on any colour background (within reason) and still look good.
The other colour bit-rates are generally only useful for historical purposes and a waste of memory in most cases. 8 bit includes 256 colours and displays very much like a GIF file in that is has a limited palette – but can still be made to look good – but has only 1 bit or colour for transparency. For this reason it is impossible to smoothly render a curve or diagonal line without looking very jagged and stepped. It is possible to work around this using straight edges but it is very limiting for the designer and although he file size will generally be much smaller (Kb), it is barely used any more unless the client has a specific requirement for it.
4 bit icons include a very basic 16 colour palette and 1bit transparency and finally 2 bit icons consist simply of black and white (monotone) but also include 1bit transparency. It is very rare that either of these options is required or requested but they still feature as part for the Windows 7 ICO format specification.
For additional information on Windows icons please see the following Blog articles: