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.ICO File Extension

File TypeIcon File

DeveloperMicrosoft
Popularity
4.1 (79 Votes)
CategorySystem Files
FormatBinary

Binary

This file is saved in a binary format, which requires a specific program to read its contents.

What is an ICO file?

An ICO file contains an icon, which is typically used for a Windows program, file, or folder. It stores one or more images in various sizes so they can be appropriately scaled depending on their use. ICO files are similar to .CUR files, which are also used in Windows, and .ICNS files, which are used in macOS.

More Information

Screenshot of a .ico file in File Viewer Plus 2

ICO file open in File Viewer Plus 2

All icons for executable files in Windows are saved in the ICO format. Windows ICO files typically store images ranging from 16x16 to 256x256. Older ICO files only include images up to 48x48 which was previously the recommended dimensions by Windows. However, most newer icons include images up to 256x256 to accommodate screens with higher DPI.

Each image in an ICO file with less than 32 bits of color depth stores two bitmaps: 1) the AND bitmap - the image mask (which determines what part of the icon is transparent) and 2) the XOR bitmap - contains the icon which is mapped onto the image mask. Images with 32 bits of color are 24-bit images with 8-bit channels for alpha compositing purposes.

The favicon.ico file is used to store a small website logo that appears in the address bar of a web browser. If a website has a favicon.ico image, it will appear to the left of the web address when any page of the website is loaded. The favicon.ico image file must be 16x16 pixels and stored in the root directory of the website in order for the web browser to recognize it.

Common ICO Filenames

favicon.ico - A 16x16 pixel .PNG file located in the root directory of a website and containing a small icon graphic to be displayed in the Web browser's address bar.

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Programs that open ICO files
Updated 3/1/2019

About ICO Files

Our goal is to help you understand what a file with a *.ico suffix is and how to open it.

The Icon file type, file format description, and Mac, Windows, Linux, and Android programs listed on this page have been individually researched and verified by the FileInfo team. We strive for 100% accuracy and only publish information about file formats that we have tested and validated.

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