Reduce DNG files size when exporting?

I currently use PL and LR (depending on my mood…). :slight_smile:

Sometimes, I want to export denoised files from DXO as a DNG file into Lightroom. However, the files are huge! The size is especially surprising as I’m only denoising and not doing any other edits.

Is there a way to export DNG files that are smaller? Or a way to compress them?

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You’re not just denoising - you’re demosaicing. The result is going to be big:


Is there a way to compress?

There is not.



You may be interested in this recent post: DxO PureRAW 3 review - Life after Photoshop

Its focus is on PureRaw … but it discusses the (unavoidable) issue of large size of DNGs.

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…which has nothing to do with the file’s format, but with the fact that the images we get have been demosaiced.

@Soundchasr, when we replace pixels of red or green or blue info (one per pixel) by pixels of red, green and blue, we necessarily get about three times the file size, which is a physical necessity rather than something we can change. Look at it as the price we pay for DxO denoising and optical corrections. :man_shrugging:

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DNG is a file format.
A raw file captures info at a bit depth of 12 or 14 bits, after a/d conversion. Every sensel, sensor element, deals with only 1 color.
After demosaicing every pixel, picture element, contains 3 colors and can be 8 or 16 bits per color, resulting in a pixel size of 24 or 48 bits. So theoretical the image can be 24/14=1.7 or 48/1.7=3.4 times as large as the raw. Compression not included.

A DNG can also contain the solely raw file. Then it’s about the same size as the raw file.
Don’t ask me the benefits of DNG. I never uses it.


I suppose it raises a question when the same RAW file, converted with Adobe DNG Converter actually gives a smaller file, which can then be denoised successfully in PL, although not quite as well. Which leaves me asking why the export has to be so big.

…because Adobe’s DNG converter doesn’t demosaïc, but only compress (etc.) the raw image data. Check out the converter’s options. One of them can convert to linear DNG if I remember correctly and if that option is still present.

Thank you everyone for the responses. Although not ideal, I think what I’ll do is create the DNGs to edit and then delete them after. I’m ok with just having the RAW files as my backup and, if I need to, I can recreate my edits.

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That doesn’t make sense. DNG is supposed to be a universal raw files, but when it only compresses the raw data then it’s still a dedicated raw file. I’ve been searching for the possibility in Adobe’s DNG converter for linear DNG but can’t find it.


Not with me. Windows. DNG converter 13.2

What does linear (mosaikfrei) mean?


I found it. It’s part of Benutzerdefiniert(customized). Still don’t know in what context I must read it.


Just FYI, DNG converter and Adobe Raw software release is up to version 15.2 now…

That’s the Camera Raw version. DNG version is up to 1.6. For those who want to read the specs

I converted 2 files: a NEF and an ARW.
Nef original 25915kB, after conversion 25951kB, No typo.
ARW original 83522kB, after conversion 37568. Also no typo.

When using linear “mosaikfrei” whatever that means and compressed I get
Nef 95967kB
ARW 122175kB
The same when not compressed
Nef 146844kB
ARW 251928kB

Why such a huge difference with the ARW in 1). Is it the picture or the ARW?


Adobe DNG Converter, by default, creates a DNG format file with exactly the same image data as the input RAW file. It is logical the file sizes should be very similar, excepting the following potential differences:

  • Overheads of the format — tiny
  • Preview thumbnail (JPEG data) being a different size to the original — potentially significant
  • Differences in compression efficiency — potentially significant

It seems, if you want, you can tell it to

  • Leave a copy of the original RAW in the file, and
  • Linearise the data, and
  • Not use compression

I’m sure if you do all that, the PhotoLab/PureRAW files will look very trim! But… download DNG Converter, drop some files on it and click go with out fiddling first, and you’ll likely get very similar file sizes. If the DNGs are significantly smaller, it suggests the camera is not doing very good compression or including massive preview images.

PhotoLab/PureRAW have no facility to do this ‘same data’ conversion.

As already stated, PhotoLab/PureRAW demosaic the data, creating entirely new image data which is (approximately) three times the size (not counting bit depth differences, which may account for more). And that file is compressed.

I just renamed a NEF to DNG and opened it in PL without a problem.
I just wonder, if the structure of the raw image isn’t changed, what is the use of a dng? It’s still a dedicated raw image.

Preview thumbnail (JPEG data) being a different size to the original — potentially significant

Nikon adds a full size medium quality jpg to the nef.


This is what Adobe has to say about it:

I used to prefer TIFF files because they made colours look the same in other editors, while DNG files often displayed colours differently, due to the respective editor’s default rendering. As camera manufacturers update their RAW formats occasionally, DNG evolved over time…but the big players never adopted it.

Using DNG as a transfer format has one major advantage over TIFF for me: White balance. WB can be set with DNG as with RAW. And as long as colour differences exist, it is beneficial to be able to change WB and colours as with RAWs…as long as we separate things clearly, i.e. not doing colour work in DPL and other editors. As with metadata, adopting a SPOD (single point of definition) approach has its benefits.


I did read that article but I must say I see it as a sails talk. Nowhere I see what a DNG is and what the real benefits are.

Advantages of DNG files.
From what I read is the DNG a native raw file with another extension. But it’s still a native raw file.
It says that the files are around 20% smaller then the native raw file. But thats due to compression and will result in some lose of quality .
It says they’re faster for they stores a standard-size preview within the file itself. That’s with Nikon from the beginning.

Is DNG as good as RAW?

DNG and RAW files are similar in that they are both versions of raw image files. However, DNG is stored in a format that’s compatible with most editing software, and the file sizes tend to be smaller than RAW.

I don’t know how to read that. If the editing software doesn’t contain a raw converter, then the editing can only be done on the included jpg.

But here we’re dealing with a DNG that contains a linear RGB file. Info about that is hard to find. For me anyway.