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Author Topic: Nat Coalson's DNG Chat with Eric Chan  (Read 6952 times)
wolfnowl
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« on: November 29, 2011, 02:26:21 PM »
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A worth read from two list members!

http://www.natcoalson.com/blog/2011/11/29/my-adobe-dng-chat-with-eric-chan/

Mike.
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Ben Rubinstein
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« Reply #1 on: November 29, 2011, 03:01:58 PM »
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The conclusion sounds like he wasn't listening to a word Eric was saying.
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Mark D Segal
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« Reply #2 on: November 29, 2011, 03:32:31 PM »
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Mike, thanks for posting this - it is a useful reference piece. And Eric, thanks for taking the time to explain all that.
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Mark D Segal (formerly MarkDS)
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Tim Lookingbill
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« Reply #3 on: November 29, 2011, 04:41:44 PM »
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Nice of you to find and post this, Mike.

I noticed in the comments section Gene McCullagh raised some concerns about DNG I wasn't aware of concerning xmp side car files and backing up files.

So to get this straight, if I were to edit a DNG version of my Pentax K100D PEF in ACR/LR, there would be no xmp side car and the edits would be embedded in the DNG file itself? Is this correct?
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« Reply #4 on: November 29, 2011, 05:48:16 PM »
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So to get this straight, if I were to edit a DNG version of my Pentax K100D PEF in ACR/LR, there would be no xmp side car and the edits would be embedded in the DNG file itself? Is this correct?

Correct if you saved out the settings to XMP. That will update the settings in the DNG and cause the file to be marked as modified so a subsequent backup based on changed files would require the whole DNG to be backed up–even if only the settings were changed. If you use Lightroom without saving the settings to the XMP but only save it in the database, the file would not need backup because the changes would only be in the database (which would be changed and hence get a backup). Same deal for JPEG & TIFF files whose XMP is written into the file.
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aduke
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« Reply #5 on: November 29, 2011, 06:19:55 PM »
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If you use Lightroom without saving the settings to the XMP but only save it in the database, the file would not need backup because the changes would only be in the database (which would be changed and hence get a backup). Same deal for JPEG & TIFF files whose XMP is written into the file.

Jeff, that is good to know. It's a subtle aspect that I've not seen explained before.
Thanks for the information.

Alan
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wolfnowl
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« Reply #6 on: November 30, 2011, 02:56:09 PM »
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You CAN set Lightroom to automatically write changes to XMP in the preferences (it's off by default), but there's a trade-off in terms of memory usage while it's doing that.  Otherwise Ctrl/Cmd-S will handle that nicely for you.  But yes, as Jeff clearly explained, Lightroom is a database program and by default stores the information in its database (catalog).

Mike.
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RFPhotography
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« Reply #7 on: November 30, 2011, 03:23:29 PM »
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If you use only LR to process RAW files then does it matter if the information is stored only in the database and not in a sidecar file?
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john beardsworth
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« Reply #8 on: November 30, 2011, 04:08:15 PM »
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If you use only LR to process RAW files then does it matter if the information is stored only in the database and not in a sidecar file?

Note only "some of" the information is ever stored in the sidecar.
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howardm
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« Reply #9 on: November 30, 2011, 04:52:03 PM »
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maybe off topic or thread stealing (sorry)......

is there any easy way to 'convert' an xmp based LR hierarchy to a 'put the data in the .lrcat' ?  Or do I have to export everything, change settings and then reimport to a new catalog?
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RFPhotography
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« Reply #10 on: November 30, 2011, 05:04:56 PM »
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Note only "some of" the information is ever stored in the sidecar.

Not sure that matters in this context.  If a user only uses LR for the RAW adjustments, exports a TIFF/PSD (or JPEG) then does everything else in PS or some other piece of software there's no need for saving out to the XMP file.  Isn't that the case?

But if there's information related to edits made in LR that is only retained in the LR database then the XMP is useless anyway.  Isn't it? 

Does ACR work differently from LR in how it handles DNG files?  This article on the Adobe site, http://help.adobe.com/en_US/Photoshop/11.0/WSD94FB319-761D-4e9a-BC8D-24DF7EBC05B4.html seems to indicate that it is possible to save edit information to a DNG from ACR to a sidecar.  But if I read Jeff's explanation correctly, in LR that's not possible?
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Schewe
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« Reply #11 on: November 30, 2011, 05:10:52 PM »
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Does ACR work differently from LR in how it handles DNG files?  This article on the Adobe site, http://help.adobe.com/en_US/Photoshop/11.0/WSD94FB319-761D-4e9a-BC8D-24DF7EBC05B4.html seems to indicate that it is possible to save edit information to a DNG from ACR to a sidecar.  But if I read Jeff's explanation correctly, in LR that's not possible?

ACR can save out a separate .xmp text file from the ACR flyout menu, LR does not do that. But you don't really want to get into a DNG plus .xmp situation because it can become complicated, which one is correct? The xmp metadata in the DNG or in the .xmp file? Camera Raw actually has a preference setting to allow you to ignore .xmp for DNG files, LR doesn't.
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RFPhotography
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« Reply #12 on: November 30, 2011, 05:36:22 PM »
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Thanks, Jeff.  Appreciate the clarification.
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Tim Lookingbill
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« Reply #13 on: November 30, 2011, 09:14:20 PM »
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Something I've discovered about the way ACR handles xmp side cars with regard to keywording. I may have to hunt down a preference setting somewhere to change this so it doesn't happen but this is what I found so far.


I just started keywording all my Raw PEFs giving each visually descriptive names in Bridge CS3 (I don't do events or weddings, just individual fine art type images). Upon doing a search in Snow Leopard (not Bridge) using very unique keywords I know would only be embedded in certain images, all I get are the xmp side cars and NONE of the PEF images so I can see their previews. Bummer. I can do a search in Bridge and I get the image thumbnails associated with the xmp side car.

Wonder if I switched all PEF's to DNG and embedded their xmp side car info which contain edits, camera info and keywords that I'll be able to use the OS to do a search and get the same thumbnail results as Bridge.
« Last Edit: November 30, 2011, 09:21:45 PM by tlooknbill » Logged
Tim Lookingbill
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« Reply #14 on: November 30, 2011, 09:33:58 PM »
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Boo-YAH! It worked. I converted one test PEF with embedded keyword to DNG and it now shows up in an OS search using that embedded keyword.
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Nat Coalson
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« Reply #15 on: December 01, 2011, 03:28:09 AM »
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The conclusion sounds like he wasn't listening to a word Eric was saying.

Ben, I can certainly understand why you would say that. Please let me clarify the statements in my conclusion.

First, the entire purpose of my conversation with Eric was to determine if the raw data from my Canon DSLRs is being modified when converting to DNG. It just took me a long time to get around to specifically asking that.

From Eric's responses, my current understanding is that with "mainstream" DSLRs like those from Canon and Nikon, the scene-referred raw data should NOT be getting modified when it's going into the DNG. In other words, the raw data in the DNG is the same as the raw data in the original CR2. But with other cameras, this will certainly not always be the case.

If after reading Eric's responses you came to a different conclusion please help me better understand. DNG is not nearly as straightforward as I thought it was.

Thanks!
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deejjjaaaa
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« Reply #16 on: December 01, 2011, 09:20:34 AM »
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Ben, I can certainly understand why you would say that. Please let me clarify the statements in my conclusion.

Nat the whole exchange was somewhat like you were trying to "press" Eric to assure you in something for whatever reason and Eric was skillfully trying to thread the fine line between many rocks and hard places...
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Tim Lookingbill
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« Reply #17 on: December 01, 2011, 01:14:15 PM »
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Well I know from just messing around converting my Raw Pentax PEF's to DNG, I can affect the JPEG preview Bridge uses, not other apps that can open and allow viewing of the DNG file like say Apple's Preview. I get two completely different previews but that's what I got with the original PEFs as well.

The main question to answer is what exactly is happening to the preview used to edit by in each converter of choice. I know my Pentax's converter uses the camera settings it only has access to while other converters offer their own recipe according to their default settings.

But an added bonus of DNG is that Bridge CS3's main Preview Panel shows the effects of sharpening much like how it's shown in Photoshop at all zoom levels. ACR (my converter of choice) only shows sharpening effects at 100% view, but Bridge now shows it at any view depending on size of it's GUI on screen while the same edited PEF the DNG was converted from doesn't show the sharpening even when I have "Use High Quality Previews" chosen in Bridge Prefs.

Frankly what I gathered from Nat's entire article is the operative statement made by Eric..."It depends". That's nailing it down.

So the specifics between other camera models and brands in how that camera delivers Raw data for ACR/LR or any other converter to convert Raw to DNG is not specifically defined and so we're really back to square one when it comes to knowing exactly what happens.

But really as long as I can edit the DNG in my converter of choice and have it look the same and behave the same using that converter's editing tools, does it really matter knowing what happens under the hood?
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afx
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« Reply #18 on: December 01, 2011, 01:20:22 PM »
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But really as long as I can edit the DNG in my converter of choice and have it look the same and behave the same using that converter's editing tools, does it really matter knowing what happens under the hood?
Yes.
What happens a few generations down when you decide to refresh your image with another converter that does not support converted DNGs?
RAW converters get better over the years. Only the original RAW file has all the information. A normalized DNG does not.

cheers
afx
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RFPhotography
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« Reply #19 on: December 01, 2011, 01:46:07 PM »
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Yes.
What happens a few generations down when you decide to refresh your image with another converter that does not support converted DNGs?
RAW converters get better over the years. Only the original RAW file has all the information. A normalized DNG does not.

cheers
afx

This runs in opposition to what Adobe (and others) have stated. 

If I convert a raw file to DNG, what's missing?  What information is contained in the original raw that isn't carried over to the DNG?
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