Click here to launch the converter.
Some years ago, National Geographic released CD box sets with archived images of their entire magazine catalog. The files are in a proprietary format with the extension .cng.
There was a viewer included, written with Adobe AIR, a now-abandoned cross-platform runtime.
Some people still have the box set around and would like to view their information, and this lets them do so.
Fortunately, Aging Engineer on YouTube discovered that .cng files are just obfuscated .jpg files. Each byte has been XORed with 0xef. Aging Engineer wrote an Excel macro to help people convert their CNG files into JPGs for folks not comfortable with doing it themselves in any programming languages.
Unfortunately, that macro doesn't work in modern versions of Excel. (And so time marches on.)
Well, if Excel changes too much, what might not? Perhaps web browsers will provide a more stable platform. (Time will tell.)
This repository contains three files you can download to use offline:
Just download the files into a folder together, and open cng_to_jpg.html in your favorite browser circa 2020 or newer, drop your .cngs onto the handy target, and voila. If you don't want support for downloading multiple files as a zip, you can leave off zip.min.js.