Inspiring

Answered

Convert to DNG increases file size

Forum|Forum|21 days ago
June 5, 2026
4 replies
135 views

I tried the “convert to DNG” function and in INCREASED the file size. Settings were:

Only convert Raw files (obviously)
Delete originals after successful conversion
Extension: dng
Compatibility: CR 16.0 and later
JPEG Preview: None
Emebed fast load data: NO
Use Lossy compression: NO
Embed Original Raw File: NO

While I do understand the benefit of DNG over proprietary raw, for long term support, I do not think it’s a good idea to allow an increase in file size without a warning.

While the alleged open character of the dng format is a good selling point, I do not think it’s going to be an issue to open raw files in the future. Nevertheless, I appreciate that option. Therefore I think the main selling point of dng would be a higher compression yielding in smaller files.

Note: I also know that a Lossy compression would obviously output smaller files, but that’s not the point.

Correct answer Jim Wilde

I couldn’t see anywhere if you mentioned if the raw files that you converted to DNG had been edited or not. Something to bear in mind that some edits, such as Denoise and Super Resolution, can generate a lot of data which is normally stored in the lrcat.data package but which will also be stored in the .acr sidecar files for proprietary raw files or directly in the file header of DNGs when the user chooses to save metadata to XMP. Converting a raw file to DNG incorporates that “save to XMP” function, so it would be no surprise in that scenario if the “convert to DNG” operation resulted in larger file sizes.

As an example, I just converted two CR3 files to DNG. Both were around 49MB, one was unedited and produced a 45MB DNG, the other had Denoise run prior to the conversion and that resulted in a 53MB DNG.

Jim Wilde

Correct answer

Community Expert

I couldn’t see anywhere if you mentioned if the raw files that you converted to DNG had been edited or not. Something to bear in mind that some edits, such as Denoise and Super Resolution, can generate a lot of data which is normally stored in the lrcat.data package but which will also be stored in the .acr sidecar files for proprietary raw files or directly in the file header of DNGs when the user chooses to save metadata to XMP. Converting a raw file to DNG incorporates that “save to XMP” function, so it would be no surprise in that scenario if the “convert to DNG” operation resulted in larger file sizes.

As an example, I just converted two CR3 files to DNG. Both were around 49MB, one was unedited and produced a 45MB DNG, the other had Denoise run prior to the conversion and that resulted in a 53MB DNG.

Antoine HLMNAuthor

Inspiring

Excellent point! In this case, no, content-generating edits (super resolution, noise reduction or clone stamps) have not been used.

Yet, this is a very good point and idea to decrease the size of the lrcat and move those data to another drive. I should dig into this topic 😉 thanks for the heads up!

By the way, I did not see this mentioned in both article about .dng conversion… that would be a good point to mention.

Again, I’m not criticizing this function or saying it should not be used. I’m saying that, based on Adobe’s claims, it should -at least- give a warning in case of file size increases.

Anshul_Saini

Community Manager

Hi @Antoine HLMN,

Thank you for taking the time to explain your suggestion in more detail.

I understand your point. Your suggestion isn’t about whether DNG is useful, but rather about improving the user experience when the Convert to DNG operation results in a file that’s larger than the original RAW.

For anyone interested in learning more about the DNG format and its intended use, we has a detailed overview here:

https://helpx.adobe.com/camera-raw/digital-negative.html

As discussed in this thread, there are valid scenarios where converting to DNG can result in a larger file depending on the source RAW format and the data that needs to be stored. However, your suggestion that Lightroom could warn users before a conversion increases file size is a reasonable enhancement request.

Since this is a feature request rather than a bug, I’d encourage you to post it in the Feature Requests section of the Lightroom Classic Community. The team monitoring that section regularly reviews feature requests and shares them with the product team for consideration.

Including your use case and why you’d find a warning helpful will provide valuable context for the discussion.

Best,

Anshul Saini

J

Jao vdL

Community Expert

This can happen if your original raw file used lossy compression. Quite a few cameras nowadays can do that. In that case, you won’t gain space efficiency going to dng. Also I would always embed a preview.

DNG is useful as an exchange format to give people the raw file with all your edits embedded but you really don’t need to convert to dng for working with your own files in Lightroom. In general it is better in my opinion to stay with the original raw. That gives you the option to use the raw file in other software at some point as dng is not really fully supported outside of the Adobe ecosystem. While dng is an open and documented format, the edit instructions that come from Lightroom or camera raw are still proprietary in nature.

Antoine HLMNAuthor

Inspiring

Thanks Jao 😉

see my answer to Johan

JohanElzenga

Community Expert

Without you saying what the original raw file was (raw files are often compressed these days), nobody can say if the bigger size of a non-compressed DNG version is strange or completely as expected.

-- Johan W. Elzenga

Antoine HLMNAuthor

Inspiring

Hi,

I’m not saying it’s strange or not. I say a warning should be the least with this behavior. I’m talking about the “convert to dng” function (which is a library function) and not “export as” which is a share function 😉

For example: I don’t mind if “export as” TIFF or PSD would dramatically increase file size. Not the same for converting files for in-library usage.

JohanElzenga

Community Expert

Converting to DNG is not for the purpose of reducing the file size. That can happen (with uncompressed raw files), but does not have to happen. DNG is a special file type that has some advantages (and disadvantages) over proprietary raw. That is why Adobe offers this option, not as a file size reduction method. And so you don’t get a warning if that conversion doesn’t reduce, but increases the file size. But it would be a good idea if you did get a warning, of course. You can file a feature request for it.

-- Johan W. Elzenga

R

richardplondon

Community Expert

Another consideration is that sometimes a Raw converter is available which includes some supposed “special sauce” from the camera manufacturer - which may simply amount to, the ability to match specific in-camera picture modes as would otherwise have been applied to JPG output. So that is a point of comparison with converting through generalised Adobe processing. This dedicated Raw converter will accept an out of camera Raw file (from that manufacturer) but may not accept a converted DNG. Converting to DNG is one-way and irretrievable unless an entire duplicate of the out of camera Raw file is extractably embedded.

Given that my preferred converter (LrC) is for now equally happy to take in a camera original Raw as a DNG, I’ve till now been reluctant to commit such a conversion. If the proprietary file format was going to no longer be supported, but DNG was: only that would be the sort of necessity which dictates it.

BTW the separate sidecar file into which metadata is written when the Raw is proprietary: I actively prefer that it is non-embedded. This way the camera file remains always untouched, and if some edits have been written out meanwhile: my next refresh of file backup is now copying just those few changed Kb per each updated photo - not, writing an entire DNG file again for each.

Antoine HLMNAuthor

Inspiring

Exactly my point 👍🏻

While Adobe’s reps might disagree, converting to dng ends up dumbing down the file by loosing all the feature you have mentioned. The argument of future proofing the files doesn’t really hold up as modern os have no issues whatsoever to read raw files. But they have a point and if raw files could be standardised, or be dng files, that’d be great. (By the way, I wonder if Adobe charges manufacturers which include dng as options (Pentax, Sigma, …))

Long story short: imho, the main benefit of dng is file size reduction (being lossy or lossless) and an increase in file size (without warning) is a big no no.

R

richardplondon

Community Expert

That’s an interesting one about e.g. Pentax (I have one): the native DNG was fully supported as an alternative to PEF within the Pentax supplied Raw converter, when I tried this several years ago, but an Adobe converted DNG (derived from a PEF) was not. Assuming one cares about such things of course. At one stage Lightroom(C) supported PEF properly but Pentax native DNG only under generic compatibility. Believe that one was later fixed.

Those who know likely cannot say what negotiations may happen behind the scenes around DNG!

I have often seen the embedding of metadata by DNG presented as a positive advantage, but remain unconvinced.

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