P: Update DNG Preview & Metadata removes the full-sized JPEG preview

[johnrellis]

The command Metadata > Update DNG Preview & Metadata removes the full-sized JPEG preview from DNGs that contain such previews.  

To reproduce on LR 14.0.1 / Mac OS 14.6.1:

1. Download and open this catalog:

https://www.dropbox.com/s/7j2fdfmflq5fm1m/dng-preview-bug.2024-10-23.zip?dl=0

2. Select the single photo and do File > Export with these settings to export a DNG with a full-size JPEG preview back into the catalog:

3. Using Exiftool, verify that the new DNG contains a full-size JPEG preview in SubIFD2:

$ exiftool -a -G1 *.dng | egrep 'Subfile Type|Image Width|Image Height|Photometric|Compression' 
[IFD0]          Subfile Type                    : Reduced-resolution image
[IFD0]          Image Width                     : 256
[IFD0]          Image Height                    : 171
[IFD0]          Compression                     : Uncompressed
[IFD0]          Photometric Interpretation      : RGB
[SubIFD]        Subfile Type                    : Full-resolution image
[SubIFD]        Image Width                     : 5496
[SubIFD]        Image Height                    : 3672
[SubIFD]        Compression                     : JPEG
[SubIFD]        Photometric Interpretation      : Color Filter Array
[SubIFD1]       Subfile Type                    : Reduced-resolution image
[SubIFD1]       Image Width                     : 1024
[SubIFD1]       Image Height                    : 683
[SubIFD1]       Compression                     : JPEG
[SubIFD1]       Photometric Interpretation      : YCbCr
[SubIFD2]       Subfile Type                    : Reduced-resolution image
[SubIFD2]       Image Width                     : 5472
[SubIFD2]       Image Height                    : 3648
[SubIFD2]       Compression                     : JPEG
[SubIFD2]       Photometric Interpretation      : YCbCr
[SubIFD3]       Subfile Type                    : Reduced-resolution image
[SubIFD3]       Image Width                     : 2048
[SubIFD3]       Image Height                    : 1365
[SubIFD3]       Compression                     : JPEG XL
[SubIFD3]       Photometric Interpretation      : Linear Raw
[SubIFD4]       Subfile Type                    : Reduced-resolution image
[SubIFD4]       Image Width                     : 512
[SubIFD4]       Image Height                    : 341
[SubIFD4]       Compression                     : JPEG XL
[SubIFD4]       Photometric Interpretation      : Linear Raw
[SubIFD5]       Subfile Type                    : Reduced-resolution image
[SubIFD5]       Image Width                     : 256
[SubIFD5]       Image Height                    : 171
[SubIFD5]       Compression                     : JPEG XL
[SubIFD5]       Photometric Interpretation      : Linear Raw

4. Take the DNG into Develop and set Exposure = +5. 

5. In Library, select the DNG and do Metadata > Update DNG Preview & Metadata.

6. Using Exiftool, observe that the DNG no longer contains a full-size JPEG preview. The largest JPEG preview is 1024 x 683 in SubIFD1:

$ exiftool -a -G1 *.dng | egrep 'Subfile Type|Image Width|Image Height|Photometric|Compression' 
[IFD0]          Subfile Type                    : Reduced-resolution image
[IFD0]          Image Width                     : 256
[IFD0]          Image Height                    : 171
[IFD0]          Compression                     : Uncompressed
[IFD0]          Photometric Interpretation      : RGB
[SubIFD]        Subfile Type                    : Full-resolution image
[SubIFD]        Image Width                     : 5496
[SubIFD]        Image Height                    : 3672
[SubIFD]        Compression                     : JPEG
[SubIFD]        Photometric Interpretation      : Color Filter Array
[SubIFD1]       Subfile Type                    : Reduced-resolution image
[SubIFD1]       Image Width                     : 1024
[SubIFD1]       Image Height                    : 683
[SubIFD1]       Compression                     : JPEG
[SubIFD1]       Photometric Interpretation      : YCbCr
[SubIFD2]       Subfile Type                    : Reduced-resolution image
[SubIFD2]       Image Width                     : 2048
[SubIFD2]       Image Height                    : 1365
[SubIFD2]       Compression                     : JPEG XL
[SubIFD2]       Photometric Interpretation      : Linear Raw
[SubIFD3]       Subfile Type                    : Reduced-resolution image
[SubIFD3]       Image Width                     : 512
[SubIFD3]       Image Height                    : 341
[SubIFD3]       Compression                     : JPEG XL
[SubIFD3]       Photometric Interpretation      : Linear Raw
[SubIFD4]       Subfile Type                    : Reduced-resolution image
[SubIFD4]       Image Width                     : 256
[SubIFD4]       Image Height                    : 171
[SubIFD4]       Compression                     : JPEG XL

7. The test catalog contains the result of doing steps 2 - 6.

[Rikk Flohr: Photography]

Updating status - adding bug

[robertseetzen]

Hello,

I would like the preview embedded in a DNG to reflect any edits performed for this DNG. After "Update DNG Preview & Metadata" in the context menu, the preview does in fact show my edits - but instead of still being full-res as before the update (6000x4000 in this case), the preview is only 1024x683. The DNG was created with "Export" and "JPEG Preview: Full Size".  Is there any way to perform the update and still have a full res preview afterwards?

If used on a DNG created with "Convert Photo to DNG", "Update DNG Preview & Metadata" seems to not affect the preview size. In the Metadata Panel with "DNG" data displayed, it still shows 6000x4000 after the update. But other than with a DNG created via Export, OneDrive Photos isn't able to display the photo.

The DNGs are meant to be synced with OneDrive extacly as they are stored in the local library. Still, OneDrive Photos should show them with all edits done in LR. Which wouldn't be a problem (at first sight), thanks to "Update DNG Preview & Metadata". But with the tiny preview created whenever an update is performed, it's not much fun to look at the photos in OneDrive.

To explain the use case a bit more: I want friends of mine to be able to use LR Classic to organize and edit their photos without the need to export edited versions before viewing the photos online or on their mobiles. And it has to be LR Classic, due to the far superior keywording and general organize tools.

A good way to achieve this seemed to be the use of lossy compressed DNG, created by large-scale conversion of the original JPEGs. As far as I understand the general possibilities of DNG regarding previews and compression methods, this could work pretty well. But it seems to me as if LR doesn't offer much of the choices that the DNG specs allow.

Any ideas how to achieve my goals and how to force LR Classic to write full-res previews would be very welcome.

[johnrellis]

It's a bug, and I just submitted a bug report:

https://community.adobe.com/t5/lightroom-classic-bugs/update-dng-preview-amp-metadata-removes-the-fu...

I tested LR versions 13 and 12 and the bug was present in them as well. I don't know of any workarounds.

[johnrellis]

@robertseetzen, see the obscure but easy workaround here:

https://community.adobe.com/t5/lightroom-classic-discussions/p-update-dng-preview-amp-metadata-remov...

[KrishnaMaithreya]

Preview size used in "Update DNG Preview & Metadata" can be changed in "Lightroom Preferences -> File Handling -> Import DNG Creation". FYI.

[johnrellis]

@KrishnaMaithreya: "Preview size used in "Update DNG Preview & Metadata" can be changed in "Lightroom Preferences -> File Handling -> Import DNG Creation"

Thanks very much. In the recipe above, when I changed Preferences > File Handling > Import DNG Creation > JPEG Preview to Full Size, then Update DNG Preview & Metadata preserved the full-sized preview in the existing DNG.

[IFD0]          Subfile Type                    : Reduced-resolution image
[IFD0]          Image Width                     : 256
[IFD0]          Image Height                    : 171
[IFD0]          Compression                     : Uncompressed
[IFD0]          Photometric Interpretation      : RGB
[SubIFD]        Subfile Type                    : Full-resolution image
[SubIFD]        Image Width                     : 5496
[SubIFD]        Image Height                    : 3672
[SubIFD]        Compression                     : JPEG
[SubIFD]        Photometric Interpretation      : Color Filter Array
[SubIFD1]       Subfile Type                    : Reduced-resolution image
[SubIFD1]       Image Width                     : 1024
[SubIFD1]       Image Height                    : 683
[SubIFD1]       Compression                     : JPEG
[SubIFD1]       Photometric Interpretation      : YCbCr
[SubIFD2]       Subfile Type                    : Reduced-resolution image
[SubIFD2]       Image Width                     : 5472
[SubIFD2]       Image Height                    : 3648
[SubIFD2]       Compression                     : JPEG
[SubIFD2]       Photometric Interpretation      : YCbCr
[SubIFD3]       Subfile Type                    : Reduced-resolution image
[SubIFD3]       Image Width                     : 2048
[SubIFD3]       Image Height                    : 1365
[SubIFD3]       Compression                     : JPEG XL
[SubIFD3]       Photometric Interpretation      : Linear Raw
[SubIFD4]       Subfile Type                    : Reduced-resolution image
[SubIFD4]       Image Width                     : 512
[SubIFD4]       Image Height                    : 341
[SubIFD4]       Compression                     : JPEG XL
[SubIFD4]       Photometric Interpretation      : Linear Raw
[SubIFD5]       Subfile Type                    : Reduced-resolution image
[SubIFD5]       Image Width                     : 256
[SubIFD5]       Image Height                    : 171
[SubIFD5]       Compression                     : JPEG XL
[SubIFD5]       Photometric Interpretation      : Linear Raw

[johnrellis]

@KrishnaMaithreya, that preferences section File Handling > Import DNG Creation is incorrectly named, since obviously the Update DNG Preview & Metadata command isn't doing an import.

But it would be incorrect to name that section simply "DNG Creation", since the other LR commands that create DNGs ignore that preference setting entirely:

- Enhance > Denoise and Super Resolution always create medium-sized DNG previews.

- Photo Merge > HDR and Panorama only add thumbnail-sized previews (256 x 171).

So that preferences section should be correctly named "Import DNG Creation and Update Previews".

[johnrellis · Accepted solution]

@Rikk Flohr: Photography, please close this bug report, since Update DNG Preview & Metadata is working as-coded.