ICO File Definition

The ICO graphics file format, also known as .ico, is an image that is used for icons set within Microsoft Windows. These ICO files can be saved to include more than one icon size or color spectrum. The most common Microsoft or desktop size standard for icons is usually 16x16, 32x32, 48x48, and 128x128, all of course in square pixel dimensions. You can however go up to 256x256 square pixels, however there aren't many graphical user interfaces that can accommodate an ICO file of that size. What's great about ICO files, is that you can adjust the color and image compression range, and fine tune the image to exactly the format and size that you need. With regard to the history of ICO, it was first introduced with Microsoft Windows 1.0, however at the time they were confined to one size, and could only accommodate 16 colors. By the time Windows 3.0 rolled out, the ICO file format was upgraded to accommodate 8 bit colors, also known as a 256 color spectrum.