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status of this document: work in progress
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Table of Contents
Last updated: Mar 9. 2000
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 Basic
Description
Windows uses ICO files to display its Icons.
There can (and for compatibility's sake should) be more than 1 picture
in an ICO file. For general purpose ICOs there should be at least one 32x32
image using the 16 Windows colors. |
Basic
File Format
| Name |
Size |
Description |
| Reserved |
2 byte |
=0 |
| Type |
2 byte |
=1 |
| Count |
2 byte |
Number of Icons in this file |
| Entries |
Count * 16 |
List of icons |
| |
|
Width |
1 byte |
Cursor Width (16, 32 or 64) |
| Height |
1 byte |
Cursor Height (16, 32 or 64 , most commonly
= Width) |
| ColorCount |
1 byte |
Number of Colors (2,16, 0=256) |
| Reserved |
1 byte |
=0 |
| Planes |
2 byte |
=1 |
| BitCount |
2 byte |
bits per pixel (1, 4, 8) |
| SizeInBytes |
4 byte |
Size of (InfoHeader + ANDbitmap + XORbitmap) |
| FileOffset |
4 byte |
FilePos, where InfoHeader starts |
| repeated Count times |
| InfoHeader |
40 bytes |
Variant of BMP
InfoHeader |
| |
Size |
4 bytes |
Size of InfoHeader structure = 40 |
| Width |
4 bytes |
Icon Width |
| Height |
4 bytes |
Icon Height (added height of XOR-Bitmap
and AND-Bitmap) |
| Planes |
2 bytes |
number of planes = 1 |
| BitCount |
2 bytes |
bits per pixel = 1, 4, 8 |
| Compression |
4 bytes |
Type of Compression = 0 |
| ImageSize |
4 bytes |
Size of Image in Bytes = 0 (uncompressed) |
| XpixelsPerM |
4 bytes |
unused = 0 |
| YpixelsPerM |
4 bytes |
unused = 0 |
| ColorsUsed |
4 bytes |
unused = 0 |
| ColorsImportant |
4 bytes |
unused = 0 |
| Colors |
NumberOfColors * 4 bytes |
Color Map for XOR-Bitmap |
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Red |
1 byte |
red component |
| Green |
1 byte |
green component |
| Blue |
1 byte |
blue component |
| reserved |
1 byte |
=0 |
| repeated NumberOfColors times |
| XORBitmap |
see below |
bitmap |
| ANDBitmap |
see below |
monochrome bitmap |
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Raster
Data encoding
The XOR Bitmap is stored as 1-bit, 4-bit or
8-bit uncompressed Bitmap using the same encoding as BMP files. The AND
Bitmap is stored in as 1-bit uncompressed Bitmap.
Pixels are stored bottom-up, left-to-right.
Pixel lines are padded with zeros to end on a 32bit (4byte) boundary. Every
line will have the same number of bytes. Color indices are zero based,
meaning a pixel color of 0 represents the first color table entry, a pixel
color of 255 (if there are that many) represents the 256th entry. |
Raster
Data encoding for 1bit / black & white XORbitmaps and for the AND-bitmap
BitCount = 1 Compression = 0
Every byte holds 8 pixels, its highest
order bit representing the leftmost pixel of those. There are 2 color table
entries. Some readers will ignore them though, and assume that 0 is black
and 1 is white. If you are storing black and white pictures you should
stick to this, with any other 2 colors this is not an issue. Remember padding
with zeros up to a 32bit boundary (This can be up to 31 zeros/pixels!) |
Raster
Data encoding for 4bit / 16 color XORbitmaps
BitCount = 4 Compression = 0
Every byte holds 2 pixels, its high-order
4 bits representing the left of those. There are 16 color table entries.
These colors do not have to be the 16 MS-Windows standard colors. Padding
each line with zeros up to a 32bit boundary will result in up to 28 zeros
= 7 'wasted pixels'. |
Raster
Data encoding for 8bit / 256 color XORbitmaps
BitCount = 8 Compression = 0
Every byte holds 1 pixel. There are 256
color table entries. Padding each line with zeros up to a 32bit boundary
will result in up to 3 bytes of zeros = 3 'wasted pixels'. |
Portability
Since ICO Files are a derivatives of BMPs
they should be quite easily converted into two BMPs, one holding the (possibly
colored) XOR Image and one holding the monochrome AND Image. Due to the
XOR-AND-scheme which may not apply to other OS, these files are not very
portable, and were never intended to be.
2byte and 4byte entries are stored
in Intel order (Least significant byte first) |
Trademarks,
Patents and Royalties
To my knowledge: none
(please read the disclaimer) |
Cross-Checking
Software
This section is for programmers, who wish
to cross-check their implementation with others. This is an incomplete
list of programs, which are available as freeware / shareware / try-before-buy
etc.
The following software is able to decode
ICOs::
-
Windows itself (obviously not freeware)
-
most resource construction sets (included
in Windows Compilers)
The following software is able to encode ICOs
-
most resource construction sets (included
in Windows Compilers)
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Online
Resources
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Disclaimer
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This is not the official format documentation.
Although we're doing our best to keep this information as accurate as possible,
there is no way of checking all of it under all possible circumstances.
We're not taking any responsibility for the results of this information
or lack thereof. The 'trademarks, patents and royalties' section is here
just for your convenience, and is in no way complete. Please send us a
note, if you find any incorrect of missing information to fileformats@daubnet.com.
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