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robosolo
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Does syncing a lossy DNG file back to the original RAW file lose color or tone info?

Jul 27, 2012 7:09 AM

Tags: #dng #lightroom_4 #lossy

I have a RAW file that I saved a copy of as a lossy DNG. Both are present in LR 4. If I make edits to the lossy copy and then sync the edits onto the original RAW, is there any loss of either color or tone information? Or do the edits I've made in the lossy file apply in the exact same way to the RAW original?

 
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  • Currently Being Moderated
    Jul 27, 2012 7:43 AM   in reply to robosolo

    What do you see when you try it?

     

    Hal

     
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  • Currently Being Moderated
    Jul 27, 2012 8:12 AM   in reply to robosolo

    There's no reason I can see, to think this should be any different than applying LR edit metadata from one image  to another regardless of file type.

     

    Only the semantic content of the metadata is getting altered, and this is held identically inside the Catalog - even for virtual copies - as far as I know.

     

    LR will use whatever form and method is suitable for each filetype if or when (optionally) writing this out, but that is always going to be discrete from the actual image or Raw content of the file.

     
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  • Andrew Rodney
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    Apr 16, 2009
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    Jul 27, 2012 8:54 AM   in reply to robosolo

    IF I understand your question, it is will the edit instructions from the Lossy DNG will there be equal data loss to the original raw. I’d say no. There will be some data loss on the Lossy DNG, it is partially rendered where the original raw isn’t. Will the results visually be the same? As Hal said, I’d test this but I suspect they will appear the same. IF you render both out to the same size and color space to say a TIFF, I suspect there will be a difference in the actual data but you probably will not see it. The best way to test the differences is to use the Subtract process in Photoshop described here:

     

    http://digitaldog.net/files/Apply_Image.pdf

     
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  • Andrew Rodney
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    Jul 27, 2012 10:31 AM   in reply to robosolo

    I’d be careful and consider what you might be losing using Lossy DNG’s just to presumably speed up some operations. This really isn’t a fully raw file anymore.

     

    see: http://news.cnet.com/8301-17938_105-57371809-1/adobe-offering-new-reas ons-to-get-dng-religion/

     
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  • Andrew Rodney
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    Jul 27, 2012 10:38 AM   in reply to robosolo

    robosolo wrote:

     

    The lossy copy actually looks better than the original. It looks as if some edits had already been done on it during the conversion.

    I can’t replicate that. I have a DNG which was fully saved with edits. I exported to the desktop but selected Lossy DNG and re imported. I’m looking at the two in compare and note that the metadata shows one is 8 bits per color and Lossy DNG, the other 14 bits per color and the original. They look identical to me. Even zoomed 3:1. Which is what I’d expect. Maybe you need to insure you update the metadata in the original before you export to Lossy DNG and then re-import to compare.

     
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  • Andrew Rodney
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    Jul 27, 2012 11:10 AM   in reply to robosolo

    robosolo wrote:

    I guess there's no inexpensive way for me to speed up LR other than to order a new system.

    I’m in the same boat. My 2007 MacPro is sluggish with 5DMII files. I can’t run Mountain Lion.

     
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  • Currently Being Moderated
    Jul 27, 2012 1:57 PM   in reply to robosolo

    robosolo wrote:

     

    I can see a distinct difference between the DNG and the lossy DNG screen views

    I'd be curious if you could describe or post these differences.

     

     

    If the differences are often negligible, or are at least predictable, it seems like editing lossy DNGs, then transferring settings back to raw may be a viable idea for some people - maybe even a plugin to automate it.

     

     

    Rob

     
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  • Andrew Rodney
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    Aug 17, 2012 12:18 PM   in reply to robosolo

    robosolo wrote:

     

    I've been viewing those two files - the original DNG and its lossy copy - on a new high resolution monitor, and now I can see no difference between them in LR. It may have been caused by different angles of view on my old monitor. That's not to say there isn't a visual difference at some level.

    This PDF explains how you can aid yourself in seeing the differences in two identical documents (pixel dimensions) with very subtle processing differences using Photoshop’s Subtract command:

     

    http://digitaldog.net/files/Apply_Image.pdf

     
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  • Andrew Rodney
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    Aug 17, 2012 1:41 PM   in reply to robosolo

    robosolo wrote:

     

    I've had that same test image pinned to a wall right in front of me for years . Unfortunately it's a jpeg. The idea here is to compare a full RAW or DNG to its lossy DNG copy.

    What test image?. Render both YOUR images the same, then subtract the two. Until you render the data, how can you evaluate what the final output from the two options will be? Export full rez, 16-bit TIFF for DNG and Lossy DNG if you normally export 16-bit data. Then subtract the two.

     
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  • Andrew Rodney
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    Aug 18, 2012 10:10 AM   in reply to robosolo

    robosolo wrote:

    This obviously indicates that there are differences between the two files. What do those differences mean? Would a print made from lossy DNG not have the same colors as a print made from a RAW? Eventually I'll do a side-by-side print comparison, but I just wanted your opinion.

    It may mean nothing but at least you can now see where the data is different, you know there is a difference etc. I suspect you’ll not be able to see this any other way. It isn’t visible on screen, probably not on print. But by subtracting the two and using Levels, you can get some idea that there are differences and where visually in one image.

     
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