How to add filenames to descriptions/captions?

I have a library of thousands of images I need to import. All of these images have descriptive filenames. For example, 014 Today Is Monday.jpg. I want to insert the filename minus extension into the description field, without typing it myself. How can I do this?

Right now, NextGEN converts the filename to ALT text, makes it all lowercase, and adds underscores in place of spaces. For example, 014_today_is_monday. I would like to do an exact copy from the filename, keeping the capitalization and spaces intact, but removing the .jpg extension.

I found some old instructions but they’re two years old and don’t refer to version 2.

https://www.ads-software.com/plugins/nextgen-gallery/