ImageGear .NET - Updated
User Guide > File Formats and Compressions > File Formats > File Formats Reference > ICO
Full Name ICO (Windows icon)
Format ID ImGearFormats.ICO
File Extension(s) *.ico
Data Type Raster Image
Data Encoding Binary
Multi-Page Support Yes
Alpha Channel Support Single alpha channel for read/write (see Comments).
IG Metadata Update Support Page
IG Platforms Support WIN32, WIN64, Unix, Unix64, .NET, .NET64, MAC

ImageGear Supported Versions

ImageGear Supported Features

ImageGear Read Support

ImageGear Write Support

ImageGear Filter Control Parameters

Filter Control Parameter Type Default Value Available Values Description
ReadAsRGBA bool false true, false If true, ImageGear reads ICO format as RGBA (RGB with alpha channel).


More than one representation of the icon bitmap is stored in order to offer a choice of icons; the version most compatible to the output device is used. Support for read-write transparency masks has been added to the ICO filter. Transparency masks are placed into an alpha channel when the image is created. These masks can subsequently be set and applied to the main image.

The structure of an ICO file consists of four data sections: the header, the Resource Descriptor, and two representations of the image data per each icon (the color bitmap and the 1-bit masking bitmap).

The header identifies the file as an ICO and stores the number of icon images that are stored in the file.

The Resource Descriptor stores the image width and height, the number of colors used, and the offset from the beginning of the file to the image data.

The 1-bit masking bitmap defines the transparent portion of the bitmap.

ReadAsRGBA control parameter determines how ImageGear reads the 1-bit AND masks. If ReadAsRGBA is False, ImageGear reads AND mask into "Extra" channel. This mode preserves unchanged pixel values from the file. However, in this mode ImageGear displays only the XOR mask and ignores AND mask (Extra channel) during display, i.e., display is not transparent. If ReadAsRGBA is TRUE, ImageGear reads ICO files as 32 bpp RGB + Alpha. This allows transparent display.

References Used

Brown, C. Wayne, and Barry J. Shepherd. Graphics File Formats: Reference and Guide. Greenwich, CT.: Manning Publications, 1992.