iyc it's not a massive diagnostic response, simply to read the metadata associated with png chunks.
We are talking about displaying PNG chunk information in the popup caption, not only "reading" it. So yes of course, the amount of information in the response to display is critical. Although you might not think of this, I have to make the design of how this info is displayed, in a functional way. I did some tests from the below link, and the output can easily be way beyond what can fit into the caption.
https://www.nayuki.io/page/png-file-chunk-inspector
I can't just extract png chunk info and just toss everything into a caption un-formatted and unrestricted. Also, you didn't add anything about how you imagined to control the output via "options". This feature suggestion is too vague, and not useful for the majority. Besides, it's too heavy to run on all images in a folder prior to page load ... It would have to be read once the image opens (in popup). It seems like you should use a specific tool for this instead.