Which icon sizes should my Windows application's icon include?
I took some time to check it in detail. I created an icon whose images have sizes of 16, 24, 32, 40, 48, 64, 96, 128 and 256. Then I checked which image is shown. All these were done with normal 96dpi. If using a larger DPI, the larger sizes may be used (only checked this a bit in Windows 7). The results:
Windows XP:
- Explorer views:
- Details / List: 16
- Icons: 32
- Tiles / Thumbnails: 48
- Right-click->Properties / choosing a new icon: 32
- Quickstart area: 16
- Desktop: 32
Windows 7:
- Explorer views:
- Details / List / Small symbols: 16
- All other options: 256 (resized, if necessary)
- Right-click->Properties / choosing a new icon: 32
- Pinned to taskbar: 32
- Right-click-menu: 16
- Desktop:
- Small symbols: 32
- Medium symbols: 48
- Large symbols: 256 (resized, if necessary)
- Zooming using Ctrl+Mouse wheel: 16, 32, 48, 256
Windows Runtime: (from here)
- Main tile: 150x150, 310x150 (wide version)
- Small logo: 30x30
- Badge (for lockscreen): 24x24, monochromatic
- Splashscreen: 620x300
- Store: 50x50
So the result: Windows XP uses 16, 32, 48-size icons, while Windows 7 (and presumably also Vista) also uses 256-size icons. All other intermediate icon sizes are ignored (they may be used in some area which I didn't check).
I also checked in Windows 7 what happens if icon sizes are missing:
The missing sizes are generated (obviously). With sizes of 16, 32, and 48, if one is missing, downscaling is preferred. So if we have icons with size 16 and 48, the 32 icon is created from the 48 icon. The 256 icon is only used for these if no other sizes are available! So if the icons are size 16 and 256, the other sizes are upscaled from the 16 icon!
Additionally, if the 256 icon is not there, the (possibly generated) 48 icon is used, but not resized anymore. So we have a (possibly large) empty area with the 48 icon in the middle.
Note that the default desktop icon size in XP was 32x32, while in Windows 7 it is 48x48.As a consequence, for Windows 7 it is relatively important to have a 48 icon. Otherwise, it is upscaled from a smaller icon, which may look quite ugly.
Just a note about Windows XP compatibility: If you reuse the icon as window icon, then note that this can crash your application if you use a compressed 256 icon. The solution is to either not compress the icon or create a second version without the (compressed) 256 icon. See here for more info.
After some testing with an icon with 8, 16, 20, 24, 32, 40, 48, 64, 96, 128 and 256 pixels (256 in PNG) in Windows 7:
- At 100% resolution: Explorer uses 16, 40, 48, and 256. Windows Photo Viewer uses 96. Paint uses 256.
- At 125% resolution: Explorer uses 20, 40, and 256. Windows Photo Viewer uses 96. Paint uses 256.
- At 150% resolution: Explorer uses 24, 48, and 256. Windows Photo Viewer uses 96. Paint uses 256.
- At 200% resolution: Explorer uses 40, 64, 96, and 256. Windows Photo Viewer uses 128. Paint uses 256.
So 8, 32 were never used (it's strange to me for 32) and 128 only by Windows Photo Viewer with a very high dpi screen, i.e. almot never used.
It means your icon should at least provide 16, 48 and 256 for Windows 7. For supporting newer screens with high resolutions, you should provide 16, 20, 24, 40, 48, 64, 96, and 256. For Windows 7, all pictures can be compressed using PNG but for backward compatibility with Windows XP, 16 to 48 should not be compressed.
The Microsoft UX icon guideline says:
"Application icons and Control Panel items: The full set includes 16x16, 32x32, 48x48, and 256x256 (code scales between 32 and 256)."
To me this implies (but does not explicitly state, unfortunately) that you should supply those 4 sizes.
Additional details regarding color formats, which you may also find useful:
"Icon files require 8-bit and 4-bit palette versions as well, to support the default setting in a remote desktop."
"Only a 32-bit copy of the 256x256 pixel image should be included, and only the 256x256 pixel image should be compressed [as PNG] to keep the file size down."