Dashboard shows files without thumbnail: Preview Image Length=0

[ubacher]

The dashboard shows files without a thumbnail image when

Code Select Expand

[PreviewIFD]    Preview Image Length            : 0

I have over 20000 files with this problem.

The metadata contains however (also):

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[SubIFD1]       Preview Image Length            : 63190

Reloading such files does not fix the problem. Can I fix it with exiftool processor?

PS: The files seem to be mostly .dng files, some are pdf.
Metadata analyst output attached.

[Mario]

This stats does not look at metadata at all.
It looks at flags stored for a file in the database when there was

1) a problem during import (no thumbnail, invalid file whatever)
2) metadata import
2) metadata write-back

IMWS offers a v1/files/problemfiles endpoint which returns files matching one or more of these criteria.

[ubacher]

But how can I fix it? Rescanning does not.

[Mario]

The flag is reset when you rescan. At least this is how it is designed and a quick check in the source code shows as much.

Switch to debug logging.
Do a forced rescan of one file with this problem.
Check the log file for W> and E> afterwards.

Send me the image with a link back to this thread so I can check if and what the problem is.

[Mario]

Both the Windows WIC DNG codec and LibRaw report that the DNG file you have provided is not supported or damaged.
The original file is from a Nikon D-300, and then the DNG was produced with Adobe DNG Converter 10.5 at some point.
Apparently, something with the file is wrong, if neither the Windows DNG codec nor LibRaw can handle the file.

I then loaded the file in the current Adobe DNG converter (v. 14.x) and saved it as a copy, with a 100% embedded preview.
Now IMatch (via WIC) can load the file OK.

Conclusion:

IMatch is right.
The file must appear in the "no thumbnail statistic". Since it has no thumbnail because it cannot be imported.

I guess, this is a non-standard or somehow damaged DNG.
Since it was written by an old version of the Adobe DNG converter and can be read by the current version of the Adobe DNG converter, my guess is that Adobe has messed up in the past and fixed this silently at some point - and the code to handle the problem DNG files is still included in the DNG converter.

So much for "DNG is a good and robust file format". You'll never know.

[ubacher]

I (re-)installed FPV codec for dng and the problem disappeared.
When reprocessing fixed the problem for you then I think it was because the preview was then 100% - while I usually use
50% preview.

I reprocessed the files overnight and all is well.

[Mario]

I (re-)installed FPV codec for dng and the problem disappeared.

Please don't.
The FPV codecs are unsupported for many years.
The codecs included in Windows are newer and handle DNG variants and RAW formats which did not exist when the FPV codecs were updated the last time, many years ago.