Is switching to DNG worthwhile?

Question

I'm aware of the difference between RAW and DNG file formats. The RAW format is proprietary to the camera manufacturer while DNG is an open standard. DNG files can be compressed without loss of detail, and can also include the photo metadata within. Both can be edited in Photoshop.

Would DNG be considered widely used today? I have a library of photos in NEF (Nikon D50) format that I have been contemplating whether to convert.

Asked by Grant Palin

Answer

Whatever you do, do not throw away your original RAW files. DNG is not a replacement for them. Perhaps your workflow requires you to convert into DNG's, but for the love of god do not throw away the originals.

If you do, then one day you will find that you will want to use a piece of software that doesn't support the DNG format as input.

Answered by Dave Van den Eynde

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How can I convert a proprietary raw image format to Adobe DNG?

Question

I have a proprietary raw camera image format taken from a Aptina camera.

Its raw file format is 16bit per color channel, 'GRBG' mode with file extension .raw. No headers, nothing, just plan raw bayer samples. I want to convert this format to DNG, as none of the raw image decoders (dcraw, gimp, …) seem to support it.

1. Is there any tool/converter which can handle Aptina camera sensor raw bayer format, and allow me to convert it to DNG format?

2. If not, I want to write a small C code to convert it myself. Where can I find the detailed specification about DNG format, its structure etc.? Any document explaining all this DNG format?

Answer

DNG files are based on the TIFF/EP standard, ISO 12234-2, (they're essentially bitmaps with extra metadata) so if you start out with an appropriate TIFF I/O library that will get you part way, but you'll need to fill in the extra data required by DNG, which could be tricky.

Raw converters need to know more than just the pixel intensities. Other relevant information includes pixel shape and orientation, or the properties of the dyes (just knowing they go GRBG is not enough, you may need to know the precise shade (or more accurately the frequency response) of each dye to create the colour representation as this varies between manufacturers). I think DNGs handle this by means of an embedded "camera profile".

edit:

There's an open source photo management application called digiKam which can write DNG files, so your best bet would probably be to look through their source and try and rip out the DNG encoding functions.

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Will converting images to DNG improve post-processing performance in Lightroom?

Question

I would like to know if converting my RAW files to DNG will improve the overall speed of Lightroom. The most painful issue is that it takes between 5 and 10 seconds to get my 1:1 image rendered when I zoom on it. I should add that my LR is configured so that it creates the 1:1 preview during importing of the files.

I use a MacBook Pro, Canon's RAWs, Lighroom 3.2. Thanks :)

Answer

All image previews are stored as JPEG files of various sizes inside of a .lrprev file. The loading speed of the preview images will likely not change much if you switch to DNG. The benefit of DNG is that it is an open standard format, and can keep the metadata in the same file as the image data, which simplifies portability. On the flip side, you would incur not only the extra cost of generating 1:1 previews on import, but also converting from your native RAW to DNG raw.

You also have to consider that DNG stores image data in a specific way, using integer values for pixel data. That will generally work for most sensors, however there are some special sensors that use non-square bayer arrays, make use of extra luminance pixels, or might possibly use floating point numbers rather than integers to store individual pixel values. At the very least, if you convert to DNG, you should keep your original RAW images around.

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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

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).

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What's the difference between PEF and DNG RAW formats?

Question

I just recently purchased a Pentax K-r. It has two formats to shoot raw with, PEF and DNG. Are there advantages or disadvantages with using one over the other?

Answer

PEF is Pentax's proprietary RAW format. DNG is the semi-standard owned by and promoted by Adobe.

In reality, there's no practical difference. They both hold the same information. It seems like there might be an advantage in having a standard format, but as a practical matter, RAW converter software needs to be updated with information for each camera anyway, and so DNG doesn't really add much. And pretty much all software that supports Pentax cameras via DNG can also read PEF files.

In older Pentax models, PEF could be (losslessly) compressed and DNG was always uncompressed. In modern cameras, they're both compressed.

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