"Compressed - Lossless - DNG" LightRoom Import

[dudedog]

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I was wondering if anyone could give me some insight into what exactly happens if I import my M8 DNG files into LightRoom by using the following settings:

 

1) "Copy photos as Digital Negative (DNG) and import" [this is one of the drop downs in the import window]; and

2) Check "Compressed (lossless)" in the Import Options in LightRoom Preferences.

 

When I do these two things:

- the resulting "LightRoom DNG" file is about half the size [5mb vs 10mb] as just importing normally

- all images seem to adjust and behave fine in LightRoom, and

- when I open an image in CS3 from LightRoom, the resulting TIFF in CS3 is identical in size whether I do the above two things or just import the "M8 DNG" straight into LightRoom and then open it in CS3.

 

So I would be interested to know if anyone has experienced any problems importing this way, or has any specific reasons why this is not a good idea. I shoot about 1,000 to 2,000 shots per month and if there is no difference, might as well save the disc space and the backup time... thanks.

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[luigi bertolotti]

Me too noticed this feature, and maybe, surfing on the Adobe support sites, some explanation can be found (I haven't yet tried to search). My impression is that is a "proprietary - low level" file compression , i.e. a compression made at byte-format level, which doesn't cause any loss of data (something like the .zip for Office files and so), made simply for sparing disk space. Probably the compress/decompress alghoritms are Adobe proprietary and are embedded in their applications (CS3 and so)... but DNG is an industry standard format, and, maybe, if you try to open these "compressed DNGs" in some 3rd party application that manages DNG format, you can have problems.

[ho_co]

I could be way off base, but your description is similar to something that happened early on: Some folks ran Adobe DNG Converter on the already-DNG M8 files and found that: 1) the resultant files were half the size of the M8's native file; 2) Capture One could not read the compressed file, but other raw converters could.

 

The reason: As you know, Adobe envisaged two different ways to build legitimate DNG files. Leica was the first one to implement the second one, using a lookup table written into the file. (Beside the point in your case, but completing the above thought: Since Capture One had been written to accept the M8 format, it didn't expect to see the compressed format when the file identified the camera as M8, and balked.)

 

What you're doing with the 'lossless compression' turned on is in the M8's case converting to the more usual DNG format.

 

Check me on this by: 1) running DNG Converter on an original M8 file and comparing its byte size to that produced by importing it as you do; and 2) running DNG Converter on one of the files you've imported. If I'm right, all three converted files should be identical.

 

Hope this helps.

 

--HC

[cbretteville]

PhaseOne does, AFAIK, not use Adobe's libraries to read/write DNGs. This approach must have enough advantages that PhaseOne chose it. They do however then have to implement any additional support in their own code rather than rebuilding C1 with an updated library from Adobe, thus we see legit DNGs that aren't supported by C1. I think you see the same if you convert a Digilux2 raw to DNG and try to open it in C1 - it fails. I know Sandy had to tweak CornerFix to get C1 to read the DNGs that are the output from CF.

 

- Carl

[hoppyman]

I am using ACR 4.41. I noticed this too. The engine in LR and ACR is the same. I posted a query to the Adobe Raw user forums. The reply was that ACR (or LR presumably) is using lossless compression which is more efficient than the camera's firmware. No data is lost. In my case it happened when I opened DNGs because I had altered a setting regarding previews and hence the Raw file was being resaved. I think that is is a positive (if unexpected) feature.

I cannot detect any difference whatsoever in the Raw files except for the size. Presumably it must be truly lossless as it is the nature of Raw files that the data does not change.

[sandymc]

The DNG specification includes two options for compression. The first is look-up table based, which Leica does implement (the famous 8-bit data), and is lossy. The second option is for lossless arithmetic encoding. A camera manufacturer can opt either to write uncompressed data, or to use one or both forms of compression.

 

A full DNG reader should be able to read DNGs that use any of no compression, or either type of compression, which is what ACR and Lightroom can do. However, a number of raw developer writers (e.g., Phase One) have chosen to implement DNG decoders that only work for specific cameras, rather than any DNG compliant file. So C1 will read an M8 DNG (8-bits, no lossless compression), but will usually blow up with anything else. C1 V4 is a bit better in this regard, it will read 16-bit files, but still has trouble with lossless compression.

 

CornerFix has the options to use all or none of the compression options, btw.

 

Sandy

[dudedog]

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Thank you all very much for this info. I guess the way I should look at it is this...

 

At this point, there is no problem with anything I would want to do in LightRoom, CS3, and perhaps most other programs. And so long as I import into LR, do most of my editing in CS3, and export out via TIFF, I'll probably be okay in the future with most plug-ins or other image editing programs I might want to use.

 

However, Capture One will not currently read the "LightRoom Compressed" DNG files, and perhaps in the future, some others might not read this format either, so unless I plan to marry everything in the future to LR and CS3, I'm probably better off staying with the full M8 DNG at this point.

 

I guess another way to look at it is this... while I am not currently planning on migrating at anytime in the near future to Capture One, or any other asset management tool / RAW converter, if I EVER want to migrate my image libraries in the future, I may be restricted from doing so because of the "LR Compressed DNG".

 

To me, this is not a restriction I think makes sense. I'm going to stay with the full M8 DNG... after all, storage space is getting cheaper and cheaper every day...

 

So thank you all very, very much for your input. Your help is greatly appreciated.

[hoppyman]

As noted by other folks that have provided really helpful information here, Capture One LE does not display DNG files that have been losslessly compressed in LR or ACR. However I have just installed Capture One 4 and it does display these files with no problems. So you may use either converter for comparison with no disadvantage now.

 

The same key that you have for using the LE that came with your M8, also works with Capture One 4. I had a minor error when I registered and their technical support people responded and fixed the problem within a couple of minutes. That is superb service, too.