ICO (file format)

ICO is the file name extension of a file format that is used in Microsoft Windows operating system to store icons. Unlike Windows bitmaps ( BMP), or many other graphics file formats, ICO files can contain multiple images, which uses the system depending on the required resolution and color depth. Other operating systems such as Linux or Mac OS X can use openly available program libraries handle it. The defined default MIME type is image / vnd.microsoft.icon.

However, this is not used as a synonym for icons, as virtually any graphic file format can be used for icons. In the X Window System is about XPM available.


The original standard resolution was 32 ​​× 32 pixels with 16 colors. With the introduction of Windows 3.0, 256 colors were possible. Each frame should contain an equal 1 -bit graphics that indicates whether each pixel should be drawn opaque or with XOR operation on the background, which can be obtained transparency or negative image of the background when the actual image of the body is black or white.

Since Windows XP icons and cursors are possible with alpha channel. The included icons usually have alpha channels and a maximum resolution of 48 × 48 pixels. Since Windows Vista ICO files can be up to 256 × 256 pixels in size and can then be compressed in the case in PNG format.

Operating System-wide use is the format of the favicon, show an icon that many web browser next to the URL or in the bookmark.

Related file formats

Several such icons can be integrated into program resources of PE and NE files. All frames are Technically in such a file labeled with a number and stored individually ( so-called Icon entries), in addition to a " table of contents " ( Group Icon ), which (in rare cases ) has a number or name, and the frames again summarizing. The individual frames specified in the alphabetical first Group Icon form the default program icon EXE files. Very similar is the case with Icon- Library files (extension: ICL), which are also based on the PE file format, but can not be executed. Again, a preview is used as the file icon.

The format of the cursor files of Windows ( CUR ) is, up to different characteristics of bytes in the file header ( magic number ) to the same format. In addition, a cursor file or information on the " hot spot" include, the point is actually clicked with. Multiple cursors can be summarized in a RIFF file to an animated cursor in the ANI file format.

ICO files can be edited using various graphics programs or converted from other formats such as CorelDraw, IrfanView, XnView or GIMP. However, such multi-purpose programs often do not support all features ( multiple frames, alpha transparency, PNG compression ) of the file format. In the case must be resorted to specialized software.