How do I create a disabled icon from an enabled one

Question

I have a bunch of icons, and I need to create grayed versions of them to be used when the corresponding command is disabled. How can I do that in an easy way, preferrably using GIMP since that is the only graphics program I have installed?

Answer 1

You could try in GIMP, Colours -> Desaturate

Answer 2

My usual in GIMP is to ensure the image is in RGB mode (Image->Mode->RGB) and use Colors->Hue/Saturation, changing the Saturation down to -50 and the Lightness up to 50.

If there is a color still prominent in the disabled image, try also adjusting the Lightness up on one of the Primary Colors in the same dialog.