Where DNG came from
DNG is Adobe's open standard RAW. It belongs to the RAW camera file family, which webp.now handles by rendering the document exactly as it would print and encoding each page as an image.
The technical picture
Compression: Lossless sensor data. Transparency: Not applicable. Animation: Not applicable. Colour: 12-14 bit linear sensor data. Typical file size relative to WebP: 20-100 MB per frame — hundreds of times a WebP.
Where it opens
Camera makers' own software, Lightroom, Capture One. This is usually the deciding factor when choosing between DNG and WebP — WebP renders in every browser but is uneven in desktop software, while DNG has a very different support profile.
Converting DNG to WebP
Developing a RAW into WebP produces a finished, viewable image at a fraction of a percent of the original size, with white balance and tone mapping applied. It is the fastest route from a memory card to something you can actually put on a web page. Keep the RAW originals. They stay the editable master with full highlight and shadow recovery latitude that no WebP export can give back.
Converting WebP to DNG
Convert WebP to DNG when the destination requires it. Expect the DNG output to be 20-100 MB per frame — hundreds of times a WebP — that difference is the price of getting a format the destination will actually accept.