THANKS for the explanation!
What is a Windows Vista icon?August 15th 2005, updated on September 8th 2005
This article pinpoints the differences between Windows Vista icons and Windows XP icons and explains how did Microsoft extend the .ICO file format.
This article is based on observations made while working with Windows Vista and Windows 7. There is no difference between Vista and Win7 icons from the technical point of view.
To understand this article you should already be familiar with Windows XP icon format.
Explorer in Windows Vista has a new ability - it can zoom the displayed items in and out. The zoom factor is set using a slider (on the panel in upper left corner) and it is continuous.
Explorer makes use of high-resolution 256x256 icons if they are available. The following screenshot of Windows Explorer shows, that Microsoft already created high-resolution version of several icons (Folder, My Computer, Network, and more...). This ability is not limited to system icons as demonstrated by a custom 'example-vista-icon' in the lower row.
Slider on the panel in left upper corner controls zoom factor.
The ability to put 256x256 image inside an icon is not new. It was possible in XP and even in previous systems. The problem is that an icon with all 12 formats would occupy more than 400kB on disk. This is considerably more than a ~25kB for a complete Windows XP icon. This problem was solved by extending the icon format.
The breaking change in Vista icons is that images in icon may be stored as PNGs. With PNG compression, the size of an icon is reduced and because PNG is loss-less and supports 8bit alpha channel, the quality of icon is not lowered.
Truecolor versions of default folder icon from Vista.
The icon contains 12 formats: 16x16, 32x32, 48x48 and 256x256 pixels, all in 16M, 256 and 16 colors.
Large versions are compressed in Vista.
Only the large images are compressed in current Vista icons. Our experiments show, that Vista will gladly accept an icon with all images compressed, but this icon would be unreadable in Windows XP or previous.
For our experiments, I have prepared an icon that mimics the format of Vista icons. That is, it has 12 images ranging from 16x16 to 256x256 pixels in all color depths. Large images are compressed. You may download this icon from the icon gallery.
At the time of writing this article, none of the major icon editors understands Vista icon format. This is no surprise as the format differs considerably.
We have prepared a special edition of RealWorld Icon Editor that fully supports Vista icons. This world-first Vista icon editor can open, extract, modify and save Vista icons. It is also possible to save the icons without compression for full compatibility with Windows XP.
THANKS for the explanation!
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