ICO (file format)
ICO is the filename extension of a file format that is used in the Microsoft Windows operating system to save icons . Unlike Windows Bitmaps (BMP) or many other graphic file formats, ICO files can contain several individual images, which the system uses depending on the required resolution and color depth. Other operating systems such as Linux or Mac OS X can also handle it with the help of open program libraries. The defined standard MIME type is image / vnd.microsoft.icon .
However, this cannot be 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.
history
The original standard resolution was 32 × 32 pixels with 16 colors. With the introduction of Windows 3.0, 256 colors were possible. Each individual image should contain a 1-bit graphic of the same size, which indicates whether the respective pixel should be drawn over the background as opaque or with an XOR operation , whereby transparency or a negative image of the background can be retained if the actual image is attached to the Position is black or white.
Icons and cursors with an alpha channel have been possible since Windows XP . The icons supplied mostly 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 optionally compressed as PNG .
The format is used across operating systems with the favicon , an icon that many web browsers display next to the URL or in the bookmarks .
Similar file formats
Several such icons can be included in the program resources of PE and NE files . From a technical point of view, all individual images in such a file are given a number and saved individually (so-called icon entries), in addition to a "table of contents" (group icon) that has a number or (in rare cases) a name and the individual images summarizes. The individual images listed in the alphabetical first group icon form the standard program icon of EXE files. The situation is very similar with Icon Library files (extension: .icl ), which are also based on the PE file format but cannot be executed. Again, a preview is used as a file icon.
The format for mouse - which also called cursor files of Windows (with the extension .cur ) - it is up to different characteristics bytes in the file header ( Magic Number ) to the same format. In addition, such a cursor file can also contain information about the so-called hot spot , i.e. the point with which the user actually clicks. In addition, several cursors in a RIFF file can be combined into a so-called animated cursor .
ICO files can be edited with various graphics programs or converted from other formats, such as CorelDraw , IrfanView , XnView or GIMP . However, not all multi-purpose programs use the full range of functions (multiple individual images, alpha transparency, PNG compression) of the file format. In this case, specialized software must be used.
Web links
Individual evidence
- ↑ Simon Butcher: MIME media type name: Image / MIME subtype name: Vendor Tree - vnd.microsoft.icon. IANA , September 3, 2003, accessed March 24, 2012 .