I used GIMP 2.4.6 for this tutorial but I think you can use any version that shows a window like this when you try to save an .ico file.
Important is that you need a square image for your icon, if the image you want make an icon of isn't square you can leave a transparent space at the top and the bottom but that wouldn't look good in every case.
Also we need to make different versions of the image, we need it in the following resolutions:
- 16x16 (list view and task bar / tray bar)
- 32x32 (symbol view)
- 48x48 (miniature view)
There are much more resolutions but these are the most common in the operation systems.
I'll tell you this first so you can take a guess if the image you want to make would be recognizable in 16x16. But except you make programs like me you wouldn't really need 16x16 and in 32x32 is more recognizable than you may think.
You can use 32x32 icons for links to programs and folders for example so you can make them look like you want.
Creating the Base Image
Create a new image with File → New, set the width and the height to 48x48 and under Advanced Options the Fill with to Transparency.
You should now have an image like this:
For easier use you can name the layer Background into 48x48 by selecting it with clicking at it once with the left mouse button and then double clicking it with the left mouse button.
Now you can open the image you want to make into an icon and crop or scale it to 48x48.
I'll just take the star I made for my test.
Making the Different Layers
If you want to make it easy for your self, you can just scale the 48x48 layer down to 32x32.
If you have drawn the image itself you should draw a new version matching for every size, this will look much better than just scaling down, trust me.
If you want to make your icon fully compatible you should make a 8bit, 16bit and this 32bit version of the layers.
(not a good idea with this one because of the different transparencys on the edges)
It's relative simple.
I just duplicated the three layers two times which makes a total of 9 layers. I ordered them again like this: 16x16, 32x32 and 48x48 then again 16x16, 32x32 and 48x48 and a third time.
Press Ctrl + S, enter in the dialog where you can select the place of the file a filename with .ico at the and and click OK, then this window should open.
Set the first three layers to 8bpp for the 256 colors versions. (256 Colors or 255 Colors + Transparency)
Set the second three layers to 24bpp for the 16bit versions. (256 steps per color channel + Transparency)
Set the third three layers to 32bpp for the 24bit versions. (256 steps per color channel + 256 step in the alpha channel (smooth transparency))
GIMP will automatically try to convert the layers down to the choosen color spans. If you want to do it yourself you can use the Colors → Posterize Filter. There you can set it to either 256 or 255 colors, depending on if you want to use transparency or not. Then you can try to use the color select tool to select only one color to turn it into another. Hard work so just let GIMP do it ^^
Now just press Save and you're done.
Thanks for reading.
