1 Load your image file

Your file isn't uploaded to the server. All processing will be done locally (in your machine).
If you are worried, you can disconnect internet or confirm the code after the page is loaded.
The max size is 256px. If exceed the limit, the pixels will be scanned neither fully nor correctly.

2 Scan the image

Take some time. If you load a large image, brower will be freezed until done.

3 Get the Colors

The file you will get is Adobe Color format.

Download colors.aco file

Information

This page is made by using HTML with plain javascript. You can modify it easily.
The source code is provided where my github. Link is here.
Why I make this page is I will create pixel art. It needs to adjust a color palette.
Example:

Thanks

I use 3rd party libraries. Thanks a lot.