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Author Topic: Converting to DNG - do you lose quality?  (Read 30943 times)
The View
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« on: July 12, 2008, 12:09:52 AM »
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One of the basic truths in image editing is, that if you convert to a different color space, you lose quality.

If you convert to a different file format, you lose quality.

Do you think, that I lose quality when I convert my Canon 40D files to DNG?

And is there a good reason to do so, or shouldn't I just keep the files as they come?

Thanks!
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ErikKaffehr
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« Reply #1 on: July 12, 2008, 01:33:07 AM »
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No, you don't loose quality
Yes, there are good reasons

- DNG contains the raw data coming from the camera it doesn't add a color space
- As the pixels are kept you will not loose quality
- You don't loose quality if you convert from one non lossy file format to another non lossy file format.
- It is actually possible to set up DNG so it will store the actual original raw-file in DNG.

The very good reason to save files in DNG that there are so many versions RAW-file formats, it is quite probable that it can be difficult to read todays RAW in perhaps five years. DNG is intended as a portable RAW-format. It is developed and maintained by Adobe but specifications are open AFAIK.

Are there any disadvantages with DNG? Sure some proprietary information is lost, if you don't use the option to save the original raw file in the image. I'm not really sure that lossless actually is lossless.

Best regards
Erik


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One of the basic truths in image editing is, that if you convert to a different color space, you lose quality.

If you convert to a different file format, you lose quality.

Do you think, that I lose quality when I convert my Canon 40D files to DNG?

And is there a good reason to do so, or shouldn't I just keep the files as they come?

Thanks!
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The View
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« Reply #2 on: July 12, 2008, 02:12:18 AM »
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No, you don't loose quality
[a href=\"index.php?act=findpost&pid=207516\"][{POST_SNAPBACK}][/a]

Am I misreading this as a contradiction?

Philosophically speaking, there is no gain without a loss. You don't lose quality vs. there isn't actually any lossless.

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Are there any disadvantages with DNG? Sure some proprietary information is lost, if you don't use the option to save the original raw file in the image. I'm not really sure that lossless actually is lossless.

[a href=\"index.php?act=findpost&pid=207516\"][{POST_SNAPBACK}][/a]

This is actually a great message by you (if I don't misread it). In the digital era we strive for anything lossless. Lossless compression, non-destructive editing.

But it looks like this is all marketing speak.

I just compared my original 40D file, converted by the not very workflow-friendly Canon DPP with the superb workflow software Lightroom's conversion.

Looks like you're taking a hit in conversion quality vs. workflow quality.

And, regarding the superb workflow format DNG, maybe one pays for this with losing, as you said, some "proprietary information".

Proprietary information. This is actually wonderfully said. Isn't anything coming from a camera regarding image quality "proprietary information".

You either have a talent for philosophy or diplomacy, or both.
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The View
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« Reply #3 on: July 12, 2008, 04:38:16 AM »
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Just erased the last import, and re-imported in original Canon RAW format CR2.

Result:

Much better.

Converting your RAW files to DNG ruins your images. Makes them lifeless, soggy, and you lose detail. The colors wash out.

For me DNG is history. Never again!
« Last Edit: July 12, 2008, 04:40:48 AM by The View » Logged

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ErikKaffehr
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« Reply #4 on: July 12, 2008, 05:06:29 AM »
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Hi!

There is actually a lot of lossless compression. A very simple example is:

000000000 can be written 9x0. This is essentially what is called run length encoding. Takes 1/3 of the place (in this case).

Lossless encoding means that you can restore every bit in the image.

One issue is that RAW has linear encoding, so it does not use gamma. It is feasible to convert a 12 bit linear image to an 8 bit gamma encoded image without loosing any significant information, because of gamma encoded imaging is more efficient. BUT this would not be pixel for pixel equivalent with the original image. I doubt that any observer would be able to observe a difference. Such a conversion would be virtually lossless. You would not loose information but could not reconstruct the original image. Could you see the difference? Probaly not! Could you measure the difference? Absolutely! OK this may or may not be a diplomatic view.

Regarding proprietary information there is a lot of information embedded in the image, some of that information is standardized like EXIF and IPTC tags. Some tags are vendor specific. One example is the white balance information.

The issue is really that with each camera there is a new "raw" format. Will you be able to read your present "raw" files on your Mac OS X/7 or Windows 2012 computer?

Washed out colors may relate to color space. Lightroom uses ProPhotoRGB as a color space. If your Photoshop is incorrectly set up it may ignore the color profile. I don't thing DNG has anything to do with Color Profiles. It just holds pixel data and information tags.

This is not a question of diplomacy or philosophy, more about how things are. Many people of great experience and knowledge use Lightroom and DNG, like Michael Reichmann (the owner of this site) or Jeff Schewe, they both use Canon and they both know what they are doing. It is quite obvious that some people have issues with Lightroom. I don't know the reason for this. There was a gentleman on the MFDB forum who had a real bad experience.

If you write on this forum for advice you may get good or bad advice but I presume that all information is intended to be helpful.

Best regards
Erik


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Am I misreading this as a contradiction?

Philosophically speaking, there is no gain without a loss. You don't lose quality vs. there isn't actually any lossless.
This is actually a great message by you (if I don't misread it). In the digital era we strive for anything lossless. Lossless compression, non-destructive editing.

But it looks like this is all marketing speak.

I just compared my original 40D file, converted by the not very workflow-friendly Canon DPP with the superb workflow software Lightroom's conversion.

Looks like you're taking a hit in conversion quality vs. workflow quality.

And, regarding the superb workflow format DNG, maybe one pays for this with losing, as you said, some "proprietary information".

Proprietary information. This is actually wonderfully said. Isn't anything coming from a camera regarding image quality "proprietary information".

You either have a talent for philosophy or diplomacy, or both.
[a href=\"index.php?act=findpost&pid=207527\"][{POST_SNAPBACK}][/a]
« Last Edit: July 12, 2008, 06:57:52 AM by ErikKaffehr » Logged

John S C
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« Reply #5 on: July 12, 2008, 06:03:36 AM »
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Not a real scientific test, but I've converted one CR2 image into dng, and imported them both into Lightroom. I can't see any difference between the two. Even at 100%. Now it may be that they don't contain any really saturated colours, but the image has green foliage, green grass. Neutral grey vehicle body work and a deep blue flag.

Canon DPP does  produce a different result to Lightroom with regards certain images. From what I remember of the topic DPP does seem to give a warmer and more saturated conversion than Lightroom does "as standard". But this may be simply down to the individual way both applications process the initial view.
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Jonathan Wienke
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« Reply #6 on: July 12, 2008, 07:45:54 AM »
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Converting your RAW files to DNG ruins your images. Makes them lifeless, soggy, and you lose detail. The colors wash out.

For me DNG is history. Never again!

Bullshit. DNG files contain the exact same RAW data as the manufacturer's file format. If you convert an original RAW file and the DNG in ACR with the same settings, the converted images will be identical down to the last pixel value. You can verify this by pasting the versions on top of each other in PS and setting Difference blend mode.

If you got different results after converting to DNG, YOU screwed something up.
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Panopeeper
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« Reply #7 on: July 12, 2008, 10:29:45 AM »
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Converting your RAW files to DNG ruins your images. Makes them lifeless, soggy, and you lose detail. The colors wash out
Nonsense. I am working (programming, coding/encoding) native raw files as well as DNG files. I can assure you, that there is no relevant difference in the data except in a very few muddy cases (certainly not with Canons).

For example the data encoding (what you call "compression") in DNG is the very same as the one adopted in Canon CR2 raw files. The main difference is, that the DNG converter has more time and more computing power than the camera, thus it can compress more effectively.

Nevertheless, I don't see any (really none) reason to convert the 40D CR2s in DNG except the sightly reduced size, which is not enough for me. Plus, if you want to keep the original raw data, the DNG will be much larger than the CR2, and anyway it is a brainsick idea to embed the original in the converted file.
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Gabor
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« Reply #8 on: July 12, 2008, 12:33:06 PM »
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Converting your RAW files to DNG ruins your images. Makes them lifeless, soggy, and you lose detail. The colors wash out.

For me DNG is history. Never again!
[a href=\"index.php?act=findpost&pid=207548\"][{POST_SNAPBACK}][/a]
Pilot error.  Unless you select convert to linear data the data in the dng is the same as the data in the cr2.

Did your coverter have settings saved for the cr2 version and not for the dng version?

As to your original question.  It can be nice to have the full sized preview in the dng.  It can also be nice to not have side car files to lose.  It can also be helpful to convert to dng to get your files into a format that an older version of photoshop will support.  (Which is funny to use a new version of the dng converter to allow an older version of photoshop to work.)

What you lose is the ability to use some software.  Notably DPP.  (I think Nikon's software only supports NEF.)  It can be hard to tell if you care about this.  DPP is a pain to work with but does have some support for correcting lens flaws.  This was not a feature at the time I converted most of my files.
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The View
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« Reply #9 on: July 12, 2008, 09:18:45 PM »
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No idea what happened.

I just noticed from my old Pentax files, that the DNG were 50% smaller than the PEF files. Maybe that's a clue? I can't see an item in the import dialogue that allows you to mess up images the way mine were.

I'll see if I can find what went wrong.
« Last Edit: July 12, 2008, 09:28:39 PM by The View » Logged

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The View
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« Reply #10 on: July 12, 2008, 09:30:50 PM »
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Bullshit.
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Not exactly a terminus technicus, at least not in photography.
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The View
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« Reply #11 on: July 12, 2008, 09:36:02 PM »
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Hi!

There is actually a lot of lossless compression. A very simple example is:

000000000 can be written 9x0. This is essentially what is called run length encoding. Takes 1/3 of the place (in this case).

Lossless encoding means that you can restore every bit in the image.

(...)

I don't thing DNG has anything to do with Color Profiles. It just holds pixel data and information tags.


Best regards
Erik
[a href=\"index.php?act=findpost&pid=207556\"][{POST_SNAPBACK}][/a]

I see it can't be DNG's fault. Whatever it was, the difference was so striking...

And it can't be some kind of color space switch without my knowledge.

For the moment, I'll keep working with the original Canon RAW format until I know what happened.
« Last Edit: July 12, 2008, 09:37:21 PM by The View » Logged

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Panopeeper
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« Reply #12 on: July 12, 2008, 09:37:21 PM »
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I just noticed from my old Pentax files, that the DNG were 50% smaller than the PEF files
This depends on which Pentax. For example the *ist PEFs are uncompressed, the K100 and K200 PEFs  are compressed by "packing", while the K10's PEFs are encoded like Canon, Nikon, DNG. Accordingly, the proportion between the PEF and DNG sizes varies.
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Gabor
The View
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« Reply #13 on: July 12, 2008, 09:38:28 PM »
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This depends on which Pentax. For example the *ist PEFs are uncompressed, the K100 and K200 PEFs  are compressed by "packing", while the K10's PEFs are encoded like Canon, Nikon, DNG. Accordingly, the proportion between the PEF and DNG sizes varies.
[a href=\"index.php?act=findpost&pid=207735\"][{POST_SNAPBACK}][/a]

So that can't be it then, either.

And there are no "conversion settings" to convert to DNG.
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Panopeeper
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« Reply #14 on: July 12, 2008, 09:47:05 PM »
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there are no "conversion settings" to convert to DNG.
The conversion settings are under "Change Preferences" (there are not many).
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Gabor
The View
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« Reply #15 on: July 13, 2008, 01:08:29 AM »
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The conversion settings are under "Change Preferences" (there are not many).
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CHANGE preferences? You mean the preferences pane with the Command comma shortcut in "lightroom" menu?

I actually only found export settings, color space for exporting to external editors, etc.
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Nick Rains
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« Reply #16 on: July 13, 2008, 06:15:29 AM »
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Am I misreading this as a contradiction?

Philosophically speaking, there is no gain without a loss. You don't lose quality vs. there isn't actually any lossless.
This is actually a great message by you (if I don't misread it). In the digital era we strive for anything lossless. Lossless compression, non-destructive editing.

[a href=\"index.php?act=findpost&pid=207527\"][{POST_SNAPBACK}][/a]

CR2 files are already compressed - why do you think they vary in size? If you don't believe me see for yourself - or do the maths ( 2 bytes per photo site x megapixel rating ie 12mp should be a 24Mb file, except it ain't) . You'll find that ones with lots of detail are bigger than ones with big smooth areas - just like jpegs.

DNG files simply store the exact same RAW data in a new 'box' with a nice jpeg preview based on the RAW adjustment defined in your RAW converter (ACR) plus a set of instructions comprising the settings used to adjust it.  That's all - converting to DNG does not compress or alter anything in the RAW data.

What you are seeing is different conversions being applied to the same data - this is what you need to attend to.
« Last Edit: July 13, 2008, 06:19:51 AM by Nick Rains » Logged

Nick Rains
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« Reply #17 on: July 13, 2008, 02:13:02 PM »
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CHANGE preferences? You mean the preferences pane with the Command comma shortcut in "lightroom" menu?
Were you converting the CR2 in DNG via LR? SOrry, I have no idea, how that works.

I am using the stand-alone DNG converter, which has a "Change Preferences" button; that's what I was referring to.
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Gabor
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« Reply #18 on: July 13, 2008, 02:25:01 PM »
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Were you converting the CR2 in DNG via LR? SOrry, I have no idea, how that works.

I am using the stand-alone DNG converter, which has a "Change Preferences" button; that's what I was referring to.
[a href=\"index.php?act=findpost&pid=207875\"][{POST_SNAPBACK}][/a]

Which one do you use?

I converted to DNG using the LR setting "convert to DNG and import".
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DarkPenguin
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« Reply #19 on: July 13, 2008, 02:49:08 PM »
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Adobe DNG Converter.  You can get it bundled with ACR at the Adobe site.  It is just a standalone executable.
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