Time to be with your loved ones

Time to be with loved ones

by sat

submit your photo


Hall of Fame
View past winners from this year

Please participate in Meta
and help us grow.

Take the 2-minute tour ×
Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It's 100% free, no registration required.

I'd like to convert all my ARW (Sony) files to DNG for several reasons, but the only thing keeping me back from doing it is the fear of losing useful metadata during the conversion. I know that the image it's self is completely safe during the conversion but what about proprietary maker noteS? Will those stay too? And even if they do, are they actually useful and can be actually used by something other then Sony's own RAW converter?

P.S. I'm using Ubuntu so I'd prefer to use KipiPlugins' DNG converter because from what I understand it does everything the Adobe converter does, but if I'm wrong I can use Adobe's instead.

EDIT:

It looks like the LensID does carry over! With the ARW and the DNG files converted by Kipiplugins' built in converter, info is stored as "Exif.Sony.0x___". With Adobe's official converter, it moves the info to more logically named fields in the XMP, such as "LensID" and "Lens".

Now that I've figured it out, I think I might use Adobe's Official converter, just because I prefer how it reorganizes the Exif Data.

I'm not fully convinced though and I'd like to hear others take on all this.

share|improve this question
    
Why not just try it on a copy of one of your raw files? –  John Cavan Dec 30 '10 at 12:09
2  
That would not answer his questions, as (missing/additional) metadata tends to be invisible until seen with the right program :) –  Leonidas Dec 30 '10 at 12:39
2  
Why did you want to convert to DNG in the first place? –  Rowland Shaw Dec 30 '10 at 13:04
1  
@Leonidas - Presumably he has something to look at the EXIF or he wouldn't care in the first place... :) –  John Cavan Dec 30 '10 at 14:38
    
I just looked at both a ARW file and a DNG file's EXIF, and they both have the same "Exif.Sony.0x____" fields with the same data. So does this mean everything is being carried over or just that my Exif view doesn't see the proprietary Exif stuff? –  RPG Master Dec 30 '10 at 23:44
show 3 more comments

4 Answers

up vote 12 down vote accepted

Your answer can be found at this forum site, but the short is, you will lose some EXIF information, the lens id in particular, but the normal EXIF will be there (IE, aperture, focal length, exposure time, flash firing).

share|improve this answer
    
I just looked at both a ARW file and a DNG file's EXIF, and they both have the same "Exif.Sony.0x____" fields with the same data. So does this mean everything is being carried over or just that my Exif view doesn't see the proprietary Exif stuff? –  RPG Master Dec 30 '10 at 23:44
add comment

DNG can be a rather complex beast. The file format is similar to TIFF, in that it is not specifically an image format itself, but more of a container. A "normal" DNG image will store metadata, the primary image in TIFF format, and possibly a thumbnail image. Depending on how DNG is used by any given program, the reality may differ. It is possible to store the original RAW image data in its native format inside of a DNG, and include the XMP sidecar as another file in the DNG container. Some programs store the original RAW, a TIFF version, and a JPEG thumbnail, along with some metadata.

The story is not particularly simple when it comes to DNG. Generally speaking, for compatibility purposes, DNG images store primary image data in TIFF format. As such, they are not truly RAW images, as original image data must be processed to create a common, interchangeable format in TIFF. Some cameras these days output their sensor data directly into DNG format, and such manufacturers prefer to call that "true" raw format, but the simple fact of the matter is that their raw sensor data must still be transformed into an RGB format that can be used by various image editing programs.

If you want the benefit of RAW, you need to use your camera's native RAW format. The key difference between RAW images and their RGB counterparts is in the pixel data...a RAW image contains Bayer sensor array pixel data, rather than computer screen RGB triplet data. Bayer sensor pixels and computer screen pixels are not the same thing, and should be treated as distinct types of information to produce the maximum amount of quality when processing digital photos.

share|improve this answer
3  
Actually, it's TIFF/EP which is specific to raw and includes color filter (bayer filter) information for interpreting the information. It differs from TIFF in that it's an ISO standard not an Adobe administered one. So, I'm not sure that last assertion in your second paragraph is entirely correct, the DNG should contain the raw sensor data. Anyways, as a Pentax shooter, I get to choose either DNG or PEF, so I've chosen DNG and to date no Pentax shooter I'm aware of has been able to show a meaningful difference in the outcome between the two other than DNG is more widely supported. –  John Cavan Dec 30 '10 at 17:07
2  
From what I have read, DNG supports TIFF/EP, however in somewhat of a limited capacity. Every time I have read about DNG and TIFF/EP, there was always a catch clause that made it sound like DNG did not fully support everything that TIFF/EP does. Even if we do assume that DNG does fully support all of TIFF/EP, there is still the simple fact that bayer array information has to be translated into a TIFF/EP structure and data types, rather than its native structure. The only way to really, truly get "RAW" data is to use "RAW" data...direct, unprocessed, strait off the sensor. –  jrista Dec 30 '10 at 17:22
2  
The specification is here: adobe.com/products/dng/pdfs/dng_spec.pdf and one of the more interesting aspects is that DNG has a section for converted raw formats to be stored compressed in the new DNG file. In any case, DNG is based on TIFF/EP, it's not actually TIFF/EP, so my point is, I think DNG is getting the raw data off the sensor and it is not being converted for TIFF storage. –  John Cavan Dec 30 '10 at 18:33
    
I'll take a look once I get a chance...today is the culmination of a years work by multiple development teams from multiple divisions of Pearson...were releasing a GIGANTIC system interconnected over the internet and web services, and I can only hope it goes well. –  jrista Dec 30 '10 at 19:13
    
Good luck! By the way, see the site I linked below, it has a wealth of details on the DNG format. –  John Cavan Dec 31 '10 at 0:17
add comment

RAW is RAW. If you convert it to anything else, it is no longer RAW. Sure, you have more bit-depth than converting to an 8-bit format and you don't have an image yet (not all color channels are present at all pixels) but if you really want to keep your originals, you should keep your originals. Sorry if this goes against common lore but it can't be any other way.

DNG has been welcomed by many like a second coming when really it is just another proprietary file-format. It belongs to Adobe rather than a camera manufacturer. The only real benefit is that it is publicly documented.

The downsides are many because it is removed from the camera. Sure, it could (but in fact it does not) contain all the data from the camera sensor but it does know how the camera works. It has information on color primaries and special header fields to tell whether the sensor as a Fuji-style pixel alignment (pixels not arranged in a grid) but imagine all the present and future possibilities. The camera itself knows how pixels are arranged, how they respond to light (some may be more or less sensitive based on their position, some may be hot/dead, etc.).

Honestly, I'd rather see cameras produce a losslessly compressed high bit-depth image (say 16-bit PNG) in the camera than anything else. The output could then be unambiguously interpreted everywhere and would have been processed with all the camera knows about itself.

share|improve this answer
2  
DNG is a raw format, the TIFF/EP standard on which it is based is specific to raw image capture. –  John Cavan Dec 30 '10 at 17:09
3  
I realize it is hard to explain, so let's try an example: Imagine a camera sensor is less sensitive towards the edge of the sensor, what goes in the DNG? Option 1) The RAW data exactly read from the sensor which results in an image that looks dark along the edges in DNG viewers. Option 2) The RAW data is corrected for the fall-off and stored in the DNG file. In this case, the file looks OK but you don't have the original data in the pure sense. Most cameras do the latter because there are things that depend on that particular camera (not the model, THAT exact camera) like hot/dead pixels. –  Itai Dec 30 '10 at 18:53
3  
@John - Indeed, it has been established, DNG is less than RAW. Please read through my answer and comments carefully. The present version of DNG can store RAW data from any sensor, I agree. However, this is not sufficient because it separating data from the process of understanding that data. Vendors either have to produce data which will be correctly interpreted by DNG readers by transforming the RAW data OR give the RAW data and face inconsistent output, including from camera to camera because of sensor-corrections built into cameras as part of the QA process. –  Itai Dec 30 '10 at 21:21
3  
Then there is the issue of sensor construction. Some sensors are designed quite differently and will produce data that cannot be interpreted properly by the same process as other DNGs. That is why the fields are there for SuperCCDs which use octagonal sensors which are not lined up in a grid. Then you have the SR variety which used two type of photosites or gets two samples per photosites (depending on the generation). EXR sensors can also read half their pixels partway through an exposure. If you put that data in a DNG without compensating only proprietary software will read it! –  Itai Feb 8 '11 at 19:48
3  
Judging from the length of this thread, I'm having trouble explaining it. The main point is that even DNG software needs to be updated to support each camera because they have to be able to interpret the data placed in DNG relative to its origin. There is a lot of generic stuff but as soon as data is needed above that, you need new DNG software. The whole thing masks RAW decoding issues by saying DNG format is universal so there is no need for proprietary software. I do not see a case where DNG can be better. –  Itai Oct 11 '11 at 17:29
show 18 more comments

Converting an image file from the manufacturer's raw format to .dng will strip all of the information in the maker notes section of the EXIF data. Since all Adobe products ignore the maker notes to begin with, if you only use Adobe products you will not see a difference in this respect.

There are additional things that the conversion strips as well. For example, data from masked pixels used to determine black point are not carried over into the .dng file. Instead black point is computed and 'baked in' during the conversion process. As with all raw convertors that do not use the manufacturers own proprietary and often encrypted algorithms, there is no guarantee that the conversion by the third party software will be the same as conversions that use the manufacturer's algorithms.

Since each sensor design is different, the output from the sensor must be interpreted based in the design of that sensor. As new cameras are released with new sensor designs, updates to the DNG convertor must be made to properly convert the output from the new sensor. Not all Bayer masks, for example, use the same exact colors for each of the R,G, and B filters. Some, such as newer designs from Fuji, even alter the pattern of which pixels are filtered by R, which by G, and which by B. Without the specific information of the sensor's unique design, the convertor will misinterpret the data from the sensor.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.