Windows 1.0 Icon
The Windows 1.x variant of the ICO format is used in Microsoft Windows versions 1 and 2 to define monochrome icons. It has little in common with the ICO format used by Windows 3 and above.
Files begin with a little-endian word, which is one of:
This is followed by a 12-byte header describing the icon bitmap:
|0000||DWORD||Not used (corresponds to hot spot X/Y in the Windows_1.0_Cursor format).|
|0004||WORD||Width of bitmap in pixels|
|0006||WORD||Height of bitmap in pixels|
|0008||WORD||Width of bitmap in bytes|
|000A||WORD||Not used (corresponds to cursor color in the Windows_1.0_Cursor format).|
Two bitmaps come after the header, each
csWidthBytes bytes long. The first bitmap is ANDed with the screen pattern; then the second is XORed on top of it.
A file in 'device independent' format is stored at double its eventual size (so a 32×32 icon would be saved as a 64×64 bitmap). A file in 'Both formats' format contains the header and bitmaps for the 'device-independent' version of the bitmap, followed by the header and bitmaps for the 'device-dependent' version.
- Samples can be found in the Windows 2.x DDK, or generated with the Windows 1.x / 2.x icon editor ICONEDIT.