anyone any idea about the upper question?

Hello @daverupp, sorry, this slipped off my to-do list.

DNG files are actually small JPEGs, with the actual pixel data of the raw camera sensor hidden in some extra metadata. You can open them with anything that can read JPEG, but you'll just see the thumbnail.

You might be able to read the files with imagemagick, if you configure it carefully. For example:

vips magickload thing.dng x.jpg

But you'll probably need to poke about inside imagemagick to get it working.

A better solution would be a libraw loader for libvips, as we've discussed elsewhere I think.

Hello @jcupitt
Do you know, what the problem here could be when I try to create a thumbnail out of the attached *.dng file?
I see, that the original file format was an *.ORF format and then exported somehow via lightroom... (I assume...)
(It is done via an olympus camera)

I am getting a thumbnail, but it is super low-res... do I need to set another parameter ?
--size=4096x1080 tmp.dng -o tmp_output.jpg[optimize_coding,strip]

tmp.dng.zip

with other dng formats (like from an iphone pro) it is working very good, and the thumbnail is in good quality...
thx for looking into it.
cheers dave

Yes, you can't thumbnail DNGs, it just won't work. They are not standfard images, you have to use a specialized converter.

But funny thing is, for the iphone dng images in the first zip from the original post, it is working the same way and it looks good with the quality.

DNGs are just JPG images with the raw camera data hidden in a private field, so the thumbnail you get is as good as the DNG thumbnail.

It sounds like your iphone is using a fairly large JPG as the main image, but the olympus is not.

Ahh ok. Thx for the quick answer. Maybe I have to use dcraw then for normal cameras and for the iphone ones just as it is.
all the best.

A dedicated LibRaw loader is now available on the master branch (which will be part of the upcoming 8.18 release).