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

would like one with a GUI.

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closed as off-topic by DavidPostill, Nifle, Kevin Panko, Fazer87, Matthew Williams Jan 6 '15 at 10:32

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions seeking product, service, or learning material recommendations are off-topic because they become outdated quickly and attract opinion-based answers. Instead, describe your situation and the specific problem you're trying to solve. Share your research. Here are a few suggestions on how to properly ask this type of question." – DavidPostill, Nifle, Kevin Panko, Fazer87, Matthew Williams
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up vote 0 down vote accepted

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.

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OK thank you for the recipe :) – asksuperuser May 1 '10 at 10:48

ImageMagick can do this.

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I like it thanks. Would also like one with some GUI :) – asksuperuser Apr 24 '10 at 20:35