👍:-1
If I understand correctly what you are trying is to trigger an event after user clicks on chart segment. chart.js has this prototype method getElementAtEvent(); See the documentation.
It seems as a good place to start – you could create some function to open image gallery and call it there.
And the gallery/slider implementation is a separate issue, but if you are using some of the popular ui libraries some of them have a solution for that already. Bootstrap, for example has carousel, and JQuery has many plugins for that purpose. Here are some examples. Hope this helps…