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

• Windows 3.1
• Windows NT/95

ImageGear Supported Features

• IGFilterFormatFlags.DETECTSUPPORT - autodetection
• IGFilterFormatFlags.MPAGEREADPSUPPORT - multi-page file reading
• IGFilterFormatFlags.PAGEINSERTSUPPORT - single-page file writing
• IGFilterFormatFlags.PAGEREADSUPPORT - single page file reading

ImageGear Read Support

• ImGearCompressions.NONE:
  • Indexed + Extra: 1+1, 4+1, 8+1 bpp;
  • RGB + Alpha: 32 bpp
• ImGearCompressions.RLE:
  • Indexed + Extra: 4+1, 8+1 bpp

ImageGear Write Support

• ImGearCompressions.NONE:
  • Indexed + Extra: 1+1, 4+1, 8+1 bpp;
  • RGB + Alpha: 32 bpp

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).

Comments

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.