An ICO file or image is a vector graphics file extension used to create small-size computer icon images. It is used in Microsoft Windows because of its single or multi-colored small pictures with varying color depths and sizes.
The file format can be identified using the ".ico" extension at the end of the file name. It represents various images in PNG or BMP format.
An ICO file is appropriate where applications must select the best image from a group of image files based on color, width, or size needs.
The file format is ideal when users need multiple options or metadata in a single file. Terms such as Favion or CUR are used alternately to imply an ICO file format.
History of ICO files
Microsoft Corporation developed and launched the ICO file format in 1985. It was initially incorporated into Windows 1.0 but has since evolved with the Windows Operating System.
The file format currently has new improvements and features that correspond to the varying needs of the digital world. The first ICO image type was 32x32 pixels, which only supported monochrome colors.
Later, the 256x256 pixels ICO file was launched to support additional colors. The file format also exists in different sizes, namely 16, 24, 32, 48, 64, and 96.
An ICO file was created to help support App icons in Microsoft Windows. It integrates various image icons of varying color types and sizes into a single file, enabling the displaying programs to select an ideal image for a specific use.
The file format is commonly used for desktop shortcuts, applications, and website Favicons. It mainly applies to creating third-party apps, Windows, and favicon icons displayed in webpages’ URLs.
ICO is 0.6% popular among the top 1 million websites but only used by 0.2% of websites. The file format is preferred when creating icons because it contains multiple color depths and varying image sizes.
However, its popularity rating is relatively low since it is hardly found in the most commonly used file stores.
Properties of ICO files
An ICO file or image is comprised of small icon images. It can contain multiple or a single small image with different color depths and sizes.
Structure
An ICO file or image is in vector graphics file format. Its icons can be scaled downwards or upwards to varying sizes without losing image quality. The file format is hardly pixelated.
It comprises an Icon directory (ICONDIR), which contains the ICONDIRENTRY structure for every image in the ICO file. A contiguous block with image bitmap data closely follows each image file.
The file format has the AND bitmap – the XOR bitmap and an image mask. The image bitmap data is either in PNG or Windows BMP format, which excludes the BITMAPFILEHEADER structure.
It contains multiple or a single small image with different color depths and sizes. The various sizes of an ICO image permit the scalability of each icon.
Each ICO file supports and stores images of varying sizes and types, starting from 1x1 pixel to 256x256 pixels.
The smallest icon in an ICO file has 1 pixel, a medium icon is 48 pixels, a large icon is 96 pixels, and an extra-large icon contains 256 pixels; the file’s size limit is 16.7 million colors.
The height and width of an ICO file do not exceed 256x256 pixels, making it a low-resolution file format. The file format supports a maximum bit depth of 24 bits of colors and 8 bits of transparency.
The bit-depth allows an ICO file to generate photorealistic or highly detailed icons. It also dictates the visual quality of each icon created.
ICO files comprise multiple versions of a similar image stored or saved in varying sizes with different bit-depths in a single file. It thus permits multi-sample pixels.
Storage
An ICO file format stores data in icons for folders, files, and programs. The stored data are encrypted to safeguard against unsanctioned processing or access.
Nonetheless, the storage period for an ICO file depends on the condition and storage medium.
Since data protection law allows users to store ICO images as long as they want, depending on the situation, the file information can last indefinitely when properly stored or handled.
The storage mediums for ICO files include file systems, Content Delivery Networks, cloud, and sub-directory files, folders, or programs.
Compression
An ICO image format can be compressed using TinyPNG or PNGOUT lossless compression techniques. Although the file format compression is unnecessary, Windows recommends that ICO images of 256x256 pixels be compressed as PNGs.
The ICO file’s performance is optimized when compressed and stored in PNG format. The algorithms used to compress the file ensure that the resulting image files are small and preserve their image qualities, although they are comparatively larger than JPEG or PNG.
TinyPNG or PNGOUT algorithms compress ICO files into a smaller file size. After lossless compression, the resulting ICO (PNGOUT) file is nearly an exact image.
The compressed ICO files enhance the efficient use of storage space, but the large number of icons prolongs or increases website loading times.
Vector graphics, TinyPNG, and PNGOUT compression algorithms do not support variable compression. Their compression assumes the PNG compression process. When compressing an ICO file, the compressed image precisely restructures the original image.
The compression process uses delta encoding for each image line of pixels. The current pixels are programmed according to the pixels within the containers.
However, since the compressed ICO file is stored as PNG, the PNG file is passed over to the DEFLATE, which integrates Huffman coding with the LZ77 algorithm. The outcome is a small, high-quality compressed PNG image or file.
The ICO lossless compression is essential when web designers and developers aim to create visually appealing and more detailed graphics without distorting image information.
Editing
An ICO image can be edited using Adobe Photoshop, Microsoft Paint, CorelDraw, Illustrator, GIMP, and Photo Gallery.
The ICO image can be resized to any size the user desires using software such as Adobe Photoshop, Microsoft Paint, CorelDraw, Illustrator, GIMP, IconEdit2, Sib Icon Editor, and Photo Gallery.
Animation
An ICO file supports animation. It comprises icon features that enable enhanced customization of websites or computer apps that support multiple color depths and resolutions. Such features allow ICO files to be animated.
Animated ICO enjoys partial and extensive support across web browsers like Firefox, Safari, Edge, Opera, and Chrome.
Animate ICO uses alpha transparency, which makes it more professional, sharp, and visually presentable than animated GIFs.
Animated ICO can be customized, which is not the case with animated GIFs. Customizing animated ICO images increases user experience.
Animated ICO files can support multiple color depths and resolutions compared to GIFs.
Animated ICOs can simultaneously hold multiple frames or images, offering a video-like influence. Animated GIFs do not have this ability.
On the other hand, the disadvantage of animated ICO files is that they require higher technical skills to create. Ultimately, they result in larger file sizes that require more storage than animated GIFs.
Transparency
An ICO file or image handles transparency by allowing developers to add semi-transparent areas such as glass-like effects, anti-aliasing, and shadows to an image.
It supports icons with different transparency levels, color depths, and varying dimensions. The file format supports 8 bits of transparency.
Best use case of ICO files
- Suitable for creating website favicons (small icons) displayed close to the webpage’s URL within the address bar to help users recognize and ascertain webpages without difficulties.
- It is suitable for creating desktop shortcuts to folders, files, or apps on a computer and ensuring that the icons appear professional and high-pitched.
- Used in developing app icons that make images or user interfaces accessible and visually attractive.
- Used to ensure that app icons are optimally displayed on different screen resolutions, which makes it informal for operators to launch and recognize the apps.
Unrecommend Use Cases of ICO Files
Because of its limited color depth, it is unsuitable for creating photorealistic or highly detailed icons, forcing web designers to use other higher-color-depth image formats like AVIF.
It is unsuitable for non-Windows platforms because it is less compatible with Mobile platforms, Linux, and macOS.
ICO Browser Support
ICO enjoys support across different browsers, such as:
Opera
Chrome
Firefox
Edge
An ICO file format appears in the history lists, bookmarks, and tabs of browsers that support it.
Old browsers like Internet Explorer, which does not favor scaling icons, do not support it. Safari also supports only a preview of an ICO’s file format.
Possible ICO Browser Errors
- Errors encountered when using ICO image files include:
- Windows has inadequate resources to open the icon file
- A corrupted device driver on hardware related to ICO
- Present or past virus attacks affected your ICO file
- ‘Something has caused the ICO file to be corrupted.'
- Bad or incomplete software installation associated with ICO file
- Incorrect removal of Windows registry ICO account
- Incorrect Windows Registry ICO file paths
Advantages of ICO
- Flexibility: The ICO file format is flexible as it contains multiple images with different color depths and sizes. Hence, it disregards the need for multiple image files required for every icon version.
- Extensively Supported and Recognized: The file format has existed for a long time and is thus widely supported and recognized by different apps and platforms.
- Pleasant at any screen size or resolution: The ICO file formats allow users to store icons in multiple resolutions and sizes in one file, making it easier to design icons for display on various screen resolutions and devices.
Disadvantages of ICO
How to open ICO files
Software, including File View Pro, IrfanView, Lemkesoft Graphic Converter, Apple Preview, FastStone Image Viewer, and IvanView, can open ICO files.
Others such as Axialis Icon Workshop, Paint 3D, IcoFX, IconCool Studio, GIMP, ImageMagic, Illustrator, Adobe Photoshop, CorelDraw, and Microsoft Paint can be used to open and edit an ICO file.
The ICO file format is fully compatible with Windows Operating Systems, namely Windows 7, Windows 8, and Windows 10.
The file format is not fully compatible with non-Windows operating systems such as Mobile platforms (Android and iOS), Linux, and MacOS 10.12, 10.13, and 10.14.
Converting ICO
An ICO image file can be converted to different file types, such as PNG, JPEG, JPG, BMP, GIF, and SVG. Use online ICO converters like "convertjack" to transform your ICO file to any required format.