No color of extracted jpg from DNG

[qliu]

I have put this DNG file in google drive: https://drive.google.com/open?id=1OayJ-P_AZC11HSqpRyOtpC8MRrWlWhAc
Extracted jpg is in attachment.

You can notice this DNG image has color, but the extracted jpg doesn't.

This is the command line I tried:

Code Select Expand

exiftool -config example.config -BigImage -b --ext jpg -w .jpg .

Also tried this:

exiftool -b -PreviewImage -W! tmp.jpg RAW_LEICA_M240.DNG
Warning: [minor] Empty ApplicationNotes data - RAW_LEICA_M240.DNG
    1 output files created


Running on linux with version 10.20.

[StarGeek]

Exiftool doesn't edit the information extracted.  It appears that the embedded preview image is in greyscale.

Even Windows shows it as greyscale

[qliu]

The DNG file has color on my mac and also google drive. Color space is RGB for both DNG and extracted jpg.

For the windows preview you got, maybe they are also using exiftool to render the preview, which extracts the jpg as greyscale. Maybe it's because they don't decode the original DNG and the extracted jpg is greyscale. For this issue Mac and Google Drive are doing a better job than windows. I just want to make sure if this is a bug that exiftool didn't handle the color correctly or the embedded jpg is just a greyscale image, even though the color space shows RGB.

[Phil Harvey]

ExifTool doesn't do image manipulations.  I have no idea why the preview JPGs are B&W.

The JPEGs themselves have 3 color components, which is weird.  Looks like a Leica bug if this is straight out of the camera.

- Phil

[StarGeek]

The DNG file has color on my mac and also google drive.

Odds are that the thumbnail is being rendered from the full image.  I don't have a DNG codec installed, so Windows is probably using the embedded thumb.

Color space is RGB for both DNG and extracted jpg.

In my experience, it's pretty common for greyscale jpgs to actually be encoded with three channels.

If you want further proof, install exiv2 and run this comand 
exiv2 -ep RAW_LEICA_M240.DNG
While the resulting thumbnail is a tiff, it also is in greyscale.

[qliu]

Thanks StarGeek and Phil! I agree that sometimes we can't trust the embedded jpg too much. For this case, to get a jpg preview, it's better to go through the process of decoding and encoding of image conversion.