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Microsoft Windows Icon (.ico)

The ICO file format is integral to the user interface of Microsoft Windows, serving as the standard for icon imagery. These icons are pivotal in guiding users through the operating system's interface, offering visual cues for software programs, files, and functions. The ICO format's key feature is its flexibility; it supports various resolutions and color depths, ensuring icons remain crisp and clear on any device or display size. This scalability is essential for maintaining visual consistency and a seamless user experience across diverse hardware, from compact mobile displays to expansive desktop monitors.

The ICO files are designed to house multiple images, typically ranging from 16x16 to 256x256 pixels, catering to different viewing contexts. Within these files, each icon can exhibit a spectrum of color depths, from simple monochrome to vibrant true color, capable of displaying up to 16.7 million colors. A notable characteristic of ICO files is their support for an alpha channel, enabling icon transparency. This functionality is crucial for crafting intricate visual effects, such as shadows and anti-aliasing, allowing icons to integrate flawlessly with various backgrounds. While ICO files are predominantly associated with Windows, similar formats exist for other operating systems, like ICNS files for macOS icons. The ICO format's efficiency in bundling multiple images into a single file makes it an optimal choice for developers and designers striving to establish a unified visual identity for their software applications. Its compactness and effectiveness are unmatched, making it a staple in the realm of computer technology.

ICO Specifications

Name Microsoft Windows Icon
File Extension(s) .ico .icon
Category Raster Images
Use For Icons within the Microsoft Windows operating system, symbolize programs, files, and various functionalities.
Developer Microsoft
MIME Type(s) image/x-icon image/
License Proprietary; as it is developed and maintained by Microsoft.
File Sample(s) N/A
Compression BMP-format icons nearly always use lossless compression, but lossy methods are available. PNG icons are always compressed losslessly.
Max Dimensions 256×256 pixels
Color Modes
Mode Bits Description
Greyscale (BMP) 1 Each bit represents a single pixel, which can be either black or white.
True color (BMP) 8 and 16 Each pixel is represented by three values representing the red, green, and blue color components; each is D bits.
Indexed color (BMP) 2, 4, and 8 Each pixel is represented by a value which is one 2, 4, or 8 bits, serving as an index into the color table.
Greyscale with alpha (BMP) N/A BMP has no distinct grayscale format.
True color with alpha (BMP) 8 and 16 Each pixel is represented by four values representing the red, green, blue, and alpha color components; each is D bits.
Greyscale (PNG) 1, 2, 4, 8, and 16 Each pixel consists of a single D-bit value indicating the brightness of the greyscale pixel.
True color (PNG) 8 and 16 Each pixel is represented by three D-bit values indicating the level of the red, green, and blue color components.
Indexed color (PNG) 1, 2, 4, and 8 Each pixel is a D-bit value indicating an index into a color palette which is contained within a PLTE chunk in the APNG file; the colors in the palette all use an 8-bit depth.
Greyscale with alpha (PNG) 8 and 16 Each pixel is represented by two D-bit values: the intensity of the greyscale pixel and an alpha sample, indicating how opaque the pixel is.
True color with alpha (PNG) 8 and 16 Each pixel is comprised of four D-pixel color components: red, green, blue, and the alpha sample indicating how opaque the pixel is.
Animation No
Transparency Yes
Interlacing Yes
Metadata No
Layers No
Multipage Yes
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