Do I lose anything converting to DNG?

Question

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.

Answer 1

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).

Answer 2

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.

Answer 3

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.

Answer 4

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.