ICO

File Format
Name	ICO
Ontology	Electronic File Formats Graphics ICO
Extension(s)	.ico
MIME Type(s)	image/vnd.microsoft.icon, image/x-icon

Overview

ICO is a Microsoft Windows icon format.

ICO files can have multiple icon images of different sizes and color types in the same file, so that programs displaying them can pick the best image for a particular use.

CUR (cursor) files are in a nearly identical format with only a few bytes different.

Format

An ICO file begins with a header, and then an index listing all of the images in the file. For each image, the index contains information about its size, color format, and location in the file.

The rest of the file contains the actual images, which usually use a variant of BMP format (without the file header, and with a transparency mask). Alternatively, they may use PNG format.

See also

• Favicon

References

• ICO (Wikipedia)
• The evolution of the ICO file format: part 1, part 2, part 3, part 4