There are a lot of discussions and opinions on the internet, concerning how to save pictures in Adobe Lightroom.
There is the raw-format, coming from your camera, and the Adobe Lightroom DNG format.
Not to mention other formats like TIFF, JPG, ...
Should you keep the raw format, should you save some other format, should one keep multiple formats ?
And the original one, or the image after changes ?
I don't want to convince someone of a 'best choice', because I don't think there is one.
I only try here to compare, pro's and con's, the choice is yours.
What you do, depends on what you like, and how you feel the best at ease for the future of your precious pictures...
I limited my comparison to camera raw-format and the LR DNG-format.
The explications here after are based on lightroom version 3, and validated, where concerned, with raw-format of nikon (D300).

How lightroom works

One thing is basic for LR: It never 'overwrites' the original image with a changed image.
It keeps track of the changes you do, and maintains this change-history, leaving the original image asis.
These change-actions are called the metadata.

Metadata handling

Where these metadata is maintained depends on the options you take, and the format (DNG or not) you work on.
By default, the changes are saved to the LR library-file, as a list of actions.
But this means that, when you loose the library, you loose the track of the changes: all actions lost!

Alternatives to the LR library

To avoid the risk of loosing the changes (to avoid to depend on the library), you have 2 options:
- ask lightroom to save the metadata: explicit action per photo (Photo - Save metadate to file)
- permanently set the option to save metadata (Edit - catalog settings - metadata - automatically write metadata to XMP)
Note that this last description is not correct ! Depending on the file-format, the real action taken is different.

Metadata location and file format

Depending on the file-format working on, 'saving metadate to file' results in:
Metadata is NOT written into the image-file, as lightroom does not want to touch this format.
Or cannot (?), as there are different raw-formats depending on the camera.
Furthermore, the metadata is not saved into the image-file, but into a seperate file, the XMP-file, as a list of actions.
This file has the same name as the image, but with extension .XMP, and goes into the image directory.
DNG-format / JPG-format / others (?)...
Metadata is added to the image-file, but the bitmap is not updated, only a list of actions is added.
But in both cases, the metadate is saved 'outside the library', and thus loosing the library, or a corrupt library, is not dramatic.

Metadata interpretation

Only major problem: nobody understands/interpretes the metadata-actions, besiders lightroom itself (at least, I don't know any software that does).
In LR, when showing the picture, the metadata is interpreted, and the changes reflected as expected.
But, opening the image-file with any other software will not reflect the changes!
Even if these changes were embedded as actions in the image-file.
To have them 'permanently' reflected into the image itself, one must export the file, in LR, to any other format.
But not to RAW, because lightroom cannot write to original camera-raw format.
When you save the image to an other file in LR, LR will make a new image, with the changes applied to the bitmap itself.

LR and photoshop

As these two more or less know each other, prior principle of applying the changes to the image is applied when one, out of lightroom,
asks to open the image in adobe photoshop:
LR applies the changes to the bitmap-image, and this changed bitmap image is passed
internally to photoshop.
Photoshop does not know the seperate metadata way of working.
when you are doing changes in photoshop now, Photoshop applies the changes to the
WHen now you return to LR, the originally embedded history of changes
(metadata-format of lightroom),
are lost, as after all, it does not make any sence anymore, as the 'original' on
which the changes were to be applied, is not the same anymore !

DNG / Raw file-size

DNG's are a kind of raw format, basic info, nothing lost, just like camera raw files.
But included into the image-files is a 'preview', not being in raw format itself.
I am pretty convinced that DNG and camera raw formats work the same way. If someone could confirm ?
One big remark on this preview: Camera raw files include this preview in full size.
DNG-raw, by default in lightroom, has a smaller preview-resolution that the raw image itself.
This makes the DNG-file smaller than the camera raw image when saving an originally raw-file as dng. But that is only faked hapiness,
because you have less as well.
When including the preview in original size (possible by some setting in Lightroom), the file is about the same size as the original raw file.

DNG / Raw and thirth-party softwares

When opening a DNG-file in an other, so called DNG-aware software ( programs
understanding the DNG-format),
the embedded preview is displayed, and thus,if working with small previews in the
DNG-file, the image is displayed smaller as expected.
This is not the case with RAW-files, as these have the full-size previews.

Furthermore, watch out with this DNG-preview. Ss LR keeps his original image, and
maintains 'somewhere' his metadate, the preview is not
by default updated every time. Thus you will see in softwares showing this preview
the non-changed version of the image !

Seen the fact that lightroom understands his metadata, there is a tricky thing that one can only achieve when using DNG's:
as always mentioned above, the original image, nor the included preview image, is changed, but one can, for DNG-files, make the included preview reflect
the changes. In which case, other softwares will indeed show the image, with the changes applied.
(Photo - Update DNG preview and Metadata).
But again with the remark, that the preview-size may not be the full original's size, depending on what was asked as preview size.
As far as I could find out, this cannot be set as a global option, thus, one must do
it manually for every image changed if you want to open in an other software.

one more thing about LR libraries

even though one imports directories into the library, this pool of immages is seen as
one buch of files.
Thus, if 2 files have the same name (extension included), they cannot be
differenciated. Only one will be there, not both !


  • dng +:

    only one file, all info included
    when explicitly saving the dng-embedded preview in lightroom (manual action), the other softwares at least show
    the images with changes in their preview.
  • dng -:

    is not really smaller, unless preview is taken smaller than in raw-format,
    but then other softwares have indeed smaller preview.

    if we work on a DNG-format, what do you do with the original raw format ?
    if we delete images out of the library-interface, the dng-file is deleted, but the raw file is till hanging
    around 'somewhere'.
    so we are almost oblidged to 'not keep' the original camera-raw's, or find it back and
    delete it as well.
    saving changes means updating the dng-file (add metadata-actions), with (very) small risk
    of making the file corrupt, as we are touching it.

  • raw/xmp +:

    if we want to, we can do changes with view-nx / capture-nx (before doing something
    in lightroom of course !) or any other descent manipulation-program on the raw format.
    we have/use the real original, thus no extra work
    xmp is small, =ignorable.
    other softwares have full the size previews
    when we delete images, at least it is done on 'all copies' (there is only one)
    if we want to undo everything for an image, just delete the xmp-file
    the original is never touched.
  • raw+xmp -:

    we need the 2 files if we do not want to loose the changes.
    when setting 'auto-save' option, every raw has an xmp, even without doing
    something on the image

  • for any option -:

    other softwares do not understand the xmp format
    you always need xmp-aware software for exporting to jpg, meaning: you always need LR
  • for any option +:

    the original is never changed
    in all cases, adobe interpretes the xmp (included in the dng or external file),
    and thus change-steps can always be 'undone'.

  • finally, if one is afraid of someone stopping to support it's format: just make sure to have a copy of the related software

    My conclusion

    For me, my conclusion is that the DNG-option is not really better, it's just different.
    I work with the raw-format + XMP aside

    © Marcel Quintelier.