Read thumbnail/embedded JPEG in DNG file

I have a compressed DNG file which I can preview in the Photos app on Windows 11, possibly because there is an embedded JPEG aka thumbnail in the DNG file. Is there a way to read this thumbnail into Matlab? I figure if Windows Photos can do it, Matlab should be able to also. I can't seem to use imread as suggeted here to get the preview, however:

imread('SomeCompressedDngFile.DNG') % Error: Unable to read TIFF file "SomeCompressedDngFile.DNG". File is corrupt or image does not
contain any readable tiles.
imread('SomeCompressedDngFile.DNG', 'jpeg') % Error: 'SomeCompressedDngFile.DNG is not a jpeg file

[Walter Roberson]

https://www.mathworks.com/matlabcentral/answers/30317-open-dng-image-file

https://www.mathworks.com/matlabcentral/fileexchange/75328-read-dng-and-nef-files

https://blogs.mathworks.com/steve/2011/03/08/tips-for-reading-a-camera-raw-file-into-matlab/

Note that the TIFF content itself is probably not going to make sense as DNG images are typically compressed in a way that the Tiff class does not know how to handle.

[KAE]

Thanks for these suggestions. With the FEX program, I was getting errors ("Error using tifflib. Unable to retrieve SubIFD") with the compressed version of the DNG files, so I tried it on the uncompressed version, which fails at,

curve = uint16(info.SubIFDs{1}.LinearizationTable); 
Unrecognized field name "LinearizationTable".

But just to make sure I'm heading down the right path, I don't need to access the TIFF data, just the JPEG preview that Windows Photos can display. Is there a way to do this? [I ended up using an external program and made it as an answer in case it helps someone].

Answer 1

[KAE]

In case it helps someone, here's one approach. The program exiftool contains functions to extract the embedded jpg, and here's how to run it from Matlab,

% Run exiftool.exe from Matlab command line using system
% Format of exiftool command was taken from examples displayed if exiftool
% is run without any arguments
system('"C:\LongPathName\Image-ExifTool-12.57\exiftool" -a -b -W %d%f_%t%-c.%s -preview:all SomeDngUncompressedFile.dng');
% Creates SomeDngUncompressedFile_PreviewImage.jpg
% Read in the jpg and display it
imshow(imread('SomeDngUncompressedFile_PreviewImage.jpg')); 

This worked on the uncompressed version of the DNG files, and not on the compressed.

You can also get helpful info on the uncompressed or compressed file,

% Generate a TXT file containing information about the DNG file including
% the preview thumbnail
system('"C:\LongPathName\Image-ExifTool-12.57\exiftool" -s -s SomeDngCompressedFile.dng > SomeDngCompressedFile_EXIF.txt')

[KAE]

For some reason Matlab can't access the creation date of a DNG file using "dir" or System.IO.File.GetCreationTime('SomeDngCompressedFile.dng'). Both return the modification date. So, you can get the creation date as

follows,

system('"C:\LongPathName\Image-ExifTool-12.57\exiftool" -CreateDate SomeDngCompressedFile.dng')

But it will be very slow on large files, see here.

[Walter Roberson]

https://unix.stackexchange.com/questions/87265/how-do-i-get-the-creation-date-of-a-file-on-an-ntfs-logical-volume talks about alternatives for windows

[KAE]

Using "system" or "!" from Matlab on my Windows machine resulted in 'getfattr' is not recognized as an internal or external command.' Same error for "ntfsinfo". What am I missing?

[Walter Roberson]

It looks like the answer might be to use .NET

System.IO.File.GetCreationTime(PATH)

https://learn.microsoft.com/en-us/dotnet/api/system.io.file.getcreationtime?view=net-7.0

[KAE]

Oddly, that is also showing the file modification date, see here. My final workaround will likely be outside of Matlab and I'll post it when I figure it out! Thank you for all your help.