Converting JPEG to DNG

In discussing non-destructive JPEG editing in Lightroom and Camera Raw, I mentioned that it’s possible to convert JPEG files into DNG–a format previously limited to raw data from camera sensors.  Why do the new tools allow this, and why might it be useful?  Here’s some perspective from Tom Hogarty:

It’s been almost a year since Lightroom introduced the ability to convert TIFF and JPEG files to the Digital Negative (DNG) format. This does not mean that Adobe is magically converting output-referred TIFF/JPEG files into mosaic data that has all of the flexibility of native raw files. These converted JPEG/TIFF files are not raw files at all.

So, why allow the conversion?

As Lightroom and now Adobe Camera Raw provide non-destructive editing of JPEG and TIFF files, the DNG format offers benefits as a non-destructive editing format in addition to its position as a raw standard. DNG is designed to efficiently store the XMP metadata block and image preview associated with a non-destructive edit. As non-destructive editing capabilities grow, the DNG format has the architecture required to grow with those capabilities regardless of the source format. For example, a JPEG image converted to DNG and non-destructively edited three different ways will be able to store three sets of editing instructions and three distinct previews for each edit.

Does this lessen DNG’s position as a raw format standard? Absolutely not. The core of public DNG specification is a standard method of storing and describing raw data. Most recently, Leica and Pentax have joined the ranks of camera manufacturers supporting DNG files natively and there are a substantial percentage of professional photographers converting their proprietary raw files to DNG for workflow or archival purposes.

So, editing a JPEG in Lightroom or ACR, then making it into a DNG, allows you to create an envelope that packages up the original bits, the editing sauce, and a rendered preview that any application can see (i.e. DNG = before + after + settings).  And, unlike a regular JPEG that contains editing data, a DNG isn’t going to be mistaken for any old file.  It stands out as something with special editing properties.

Having said all this, converting JPEG to DNG is useful, but it’s not a panacea: it makes files larger (at least for now), and it’s not something I think everyone should run out and do.  (I haven’t found a need to do it myself.)  It’s an option, however, and one that could grow more useful in the future.

0 thoughts on “Converting JPEG to DNG

  1. Hi John,
    We’ve been having a lively discussion on this topic over on the Inside Aperture site here:
    [Thanks for the heads-up, Trace. I’ll read through it shortly. –J.]
    If I understand your answer to Katrin correctly, there seems to be a difference between a TIF or Jpeg file from a scanner, and a TIF or Jpeg originating from a camera.
    [TIFF is a really broad, flexible format, and there are quite a few flavors of it (layered, with and without compression, various bit depths, GeoTIFF, etc.). The images that come off cameras are one of those. –J.]
    Scanning an image from an Epson 3200 flatbed into Photoshop, then saving it out as both a TIF version, and a Jpeg version, then using DNG Converter 3.7 to convert them to .dng format gives an error message saying there is no RAW file to convert. Seems you can’t make DNGs from scanned files.
    [Actually it’s just that the converter doesn’t support converting non-raw files to DNG. I think you should be able to convert those files using Lightroom or ACR. So, this limitation has to do with the state of the converter, not with the inherent possibilities of converting to DNG. –J.]
    I also wonder what happens if /when Adobe decides to discontinue support for a particular camera model, will the ACR/DNG conversion code for that particular model be unavailable,making future versions of ACR/DNG Converter (and consequently Lightroom, etc.) unable to access these “older” DNGs? Appears if a camera is not supported by Adobe (as a RAW format), you can’t make a DNG out of it.
    [Well, the thing about DNG is that it’s meant to be open. Unlike other raw formats, it’s fully publicly documented. So even if Adobe gets taken out by one of those low-flying aircraft, the format will be readable & writeable in perpetuity. That means that other developers could provide a way to convert files to DNG. (Note: I haven’t heard any discussion of Adobe dropping support for any cameras. The whole point, though, is that photographers shouldn’t be dependent on any one company for support, and DNG offers a way to make that happen.) –J.]

  2. Is there currently a way to use DNG Converter app to make the jpg->dng conversion? When I’ve attempted, the UI skips over jpg files and the command-line won’t allow the conversion.
    [No, that’s not something the converter supports at the moment. I don’t see a big demand to add support, given that most of the converted JPEGs probably wouldn’t have ACR/Lightroom edits applied to them, but it’s something the team could consider. –J.]

  3. Will we be seeing Adobe write a DNG Codec for Windows Vista in the same way that Nikon, Sony, Olympus have and Canon is about to?
    Also, why is it that I can see DNG thumbnails in Apple’s OS X? Has Apple integrated DNG in OS X?
    Thank you.

  4. One of the advantages is that you can shoot in JPEG and still not have to worry about white balance all that much. In my experience it’s easier and less destructive to do it in CS3 camera RAW than it was with regular Hue Saturation / Curves / Color balance.
    Besides you get recovery / fill light, which generally works better out of the box than shadow/highlight, and vibrance which is much better than saturation for skin tones.
    And I usually find the sharpness / noise reduction on Camera RAW to be much better than most camera’s native solution.
    If we could get all that RAW latitude with a lossy compression algorithm like JPEG the world would be a better place. A quality 12 JPEG at 100% is almost indistinguishable from a TIFF and yet it’s often one third it’s size.

  5. In Lightroom I had entered many keywords for some 640×480 JPGS taken back in 2000 with my Sony Mavica. After copying these JPGs to an external drive and using them to create a new database I found that only a few of the Lightroom keywords has actually been written to the JPG metadata. I return to the original database, exported the JPGs to DNGs and found the DNGs contained ALL the keywords. After copying these DNGs to my external drive I was able to import them and ALL their keywords.
    [Hmm–with the JPEGs, did you choose Metadata->XMP->Export Metadata? For the sake of speed, Lightroom stores things like keywords only in its data (i.e. not synched with the files) until you choose to synch or export them. –J.]

  6. I find it interesting that you say DNG files created from JPEG are larger. I routinely convert Nikon RAW files to DNG and find that it creates files that are 15-20% smaller. For me, that’s a strong argument for archiving in DNG.
    [DNGs made from JPEGs are bigger than the source JPEGs because, as I understand it, the DNG spec doesn’t currently include support for much in the way of image compression. Clearly that would be a useful enhancement to the spec. –J.]

  7. I’m sorry, I’ve read through this post and the previous one linked… and yet I still don’t see how to convert a jpeg to a DNG. Have I missed something? How does one do it?
    [You can do it when saving a JPEG from Camera Raw 4 (in CS3), or inside Lightroom (I don’t recall the exact steps off the top of my head). –J.]

  8. As an addition to your explanation for Mike Young:
    RAW files are, by definition, not compressed. JPEG is, by design, compressed. You can compress a non-compressed format using lossless compression and then add some extra metadata and still have a smaller file. However, if you take a file that is already as compressed as it is going to get, then add metadata, it is naturally going to be larger that the original.

  9. > RAW files are, by definition, not compressed
    By whose definition?
    DNG is a RAW format. DNG supports compression.
    Cameras that shoot DNG aren’t going to compress them. However, you can use the Adobe DNG converter to compress them (add add resonably nice preview images).
    > Will we be seeing Adobe write a DNG Codec for Windows Vista in the same way that Nikon, Sony, Olympus have and Canon is about to?
    I don’t know about Adobe’s plans, but we are working on a WIC-based DNG decoder for Vista. Watch our website for updates.

  10. I have a D70s, and have been shooting JPEG format for a while. Is it worth it shoting in RAW format? I have also been converting my JPEGs into TIFF. Is that something I should consider? What is best for printing/ storing long time?
    [If you’re not shooting raw, you’re throwing away a lot of the sensitivity you paid for in your sensor. I shoot raw, convert to DNG on import into Lightroom or Bridge, and then edit from there. –J.]

  11. DNG is incredibly useful for storing keywords, location data, develop settings, etc. all in a single file. There are photographers like myself who have tens of gigabytes of old JPG files. It would be wonderful to be able to store all of the useful information that Lightroom has inside of a DNG file, rather than having to worry about that data being lost when you take it to a new computer or send it to somebody else. Please just let us convert JPG to DNG with the Adobe DNG converter.

  12. Thanks for teaching us about this use. I thought converting jpg to dng was crazy, but if I understand, it could be nice once and a while to convey the original with edits to someone else non-destructively. Cool!

  13. Hey, amateur photographer here. It’s a big hobby of mine, but I’m not a professional. I have adobe lightroom 3. All my pictures are imported as CR2 I want to convert them, so that when I give or sell my pictures to people they will be able to see them and print them on their own computers. I’m getting really frustrated. Your help would be much appreciated. I can’t figure out how to convert to JPG form. I found out how to convert to DNG, but I have no clue if that is just as good as JPG, or if other people will be able to make copies of them on their own computers. Please help me! Thanks for your time.

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