Desktop Freeware to list all colors used in a picture?

Question

I have searched but couldn't find one (not online tool only want desktop).

would like one with a GUI.

Answer 1

http://www.irfanview.com

Is actually a desktop application, with a GUI.

besides is my favourite viewer (really fast, light weight and powerful for many things) , it allows what you need:

-Open the image with it

-Hit "i" key, or the button with the "i" in top bar, or top menu image/information.

-See on "number of unique colors" in that pop up. (leave marked allwas in that pop up dialog "autocunt")

That's it, done usually in one second or less.

EDIT: Sorry, you said "list" not count... Well, I'll leave my answer here in case is of some use.

Answer 2

ImageMagick can do this.