Extracting thumbnail/preview image from DNG file using ExifTool throws warning and produces zero-byte JPG

Question

I've got a DNG file (a photo captured by Insta360 X3: single-lens mode) and I'm trying to extract the thumbnail/preview image of it so that I'll be able to upload it to my cloud drive alongside with the DNG itself for quick preview while navigating. Here's the command that I put into my Terminal (I'm on macOS Sonoma 14.2.1 and ExifTool 12.70):

exiftool -b -thumbnailimage IMG_20240108_102844_10_012.dng > thumbnail.jpg

but it threw and produced a 0-byte thumbnail.jpg:

Warning: Invalid EXIF text encoding for UserComment - IMG_20240108_102844_10_012.dng

I also tried to extract the preview image but it gave me the same result:

exiftool -b -previewimage IMG_20240108_102844_10_012.dng > preview.jpg

What did I do wrong / what did I miss?

The DNG file here: https://icedrive.net/s/D5gkZ1yBWafYQRYNvPR7w3Q4Daaa

Answer 1

That file doesn't appear to have any preview images, or at least none that exiftool can find.

You can see a list of all previews and thumbnails with this command

exiftool -G1 -a -s -Preview:all /path/to/files/

And this exiftool example shows how to extract and save all possible previews in a file.

Exiftool's -v3 (-verbose3) option can provide a break-down of how the data is organized in a file. Using that option, there doesn't appear to be any unknown data except for the MakerNoteUnknownText which, at only 224 bytes, is too small to hold an image.

If you are sure that the file is supposed to have a preview image, you can take the file over to the exiftool forums and the author of exiftool might take a look if he has time.