How do I convert images to 16bit color?

[Snailface]

. . . with a freeware program, that is (not photoshop). Thanks, Temps!

 

[jurassicplayer]

You can resave it with GIMP.

 

[sebastiaan4489]

Paint.net (Only for Windows)

 

[rad140]

Any of the above (GIMP, Paint.Net)
You can also convert an image to a 16-bit colour bitmap in Paint.

 

[amaro]

I use Paint.Net and only convert to 8 and 24-bit.
GIMP convert but with bad image.
the best program is the PhotoELF.

 

[Snailface]

GIMP: feature missing
PAINT.net: feature missing
PhotoElf: not freeware

I found a tool (Muuntimen) that will do the conversion, but it's not very convenient. The settings reset every time it's opened -- at least it's a solution though.

Thanks everybody for your help anyway!