Lightroom DNG file size

Forum|Forum|5 years ago
June 10, 2020
4 replies
2699 views

I use Sony A7R4. an uncompressed raw file from the camera is as big as 120Mb. However, after I import this file to Lightroom and convert to DNG, the size shrinks down to about 60Mb. Is it normal? Don't I lose any data during conversion? If so, is there any way to maintain the original file size?

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Camera Raw Fan

Known Participant

I was told by someone in the industry that all the same data is there, that it gets repackaged to where there is no gaps in the information which condenses the file size.

JP Hess

Inspiring

The size differential varies from one camera manufacturer to another. The information about DNG conversion from Adobe states that space savings can be as much as 50% or more. When I convert my NEF files created by my Nikon camera I only realize About a 15% reduction in size. But I don't think it is unreasonable or unrealistic to think that the size can be reduced by 50%, and you can retain the original file and compare them and wear yourself out trying to discover any quality loss. But I seriously doubt you will be able to find any.

Curt Wrigley

Inspiring

Curious why you convert to DNG. There are lots of valid reasons; just curious

I assume you are using classic. Check that you are not checking the box called "do lossy compression" in the dng dialog. That makes the files a lot smaller but does loose some information. With that not checked the file size reduction is normally in the 30% range from the original raw.

S

Sung JoonAuthor

Participant

Thanks for the comment! Well, I use DNG just because I thought it was the best way to edit photos in Lightroom. Silly answer... Anyway, I do use the newest version of Lightroom Classic CC in which I couldn't fine 'the box called <do lossy compression> in the dng dialog.' I instead found the "embed original raw file' check box in the <file handling> window of <Preferences>. When I check it, the size between the orginal raw and the converted DNG are about the same. But I gather it is unchecked by default.

Camera Raw Fan

Known Participant

For sony users there is a minor penalty for converting to DNG. Sony's raw files use a pixel shifting tech that can be stacked for improved range. If you convert them to DNG before stacking in sonys sw you loose that particular sony feature. Their sw can however stack them and output the result as a DNG.

I have a friend who is in the industry of how data formats works, and this person told me that the data is all the same. It simply gets repackaged without gaps. Gaps or spaces increase the file size. Another thing to consider is that proprietary raw files may come with extra unnecessary information. As an example, sometimes raw files will come with partially demosaiced information. And with some software it might come with fully demosaiced meta-data info for all three channels. I've come to believe that there is a lot of information that is under the hood, so to speak, that is unnecessary to process a DNG perfectly.
Take a look at a enhanced DNG and the file gets enormous! What is likely going on there is that the original Raw data is there, but also all of the information for all three channels of the enhanced raw file. Which then likely gets applied when the image is rasterized. And is used all along for the preview we see when adjusting the raw file.

Rob_Cullen

Community Expert

(Disclaimer: Not a Sony user.)

I downloaded a test ARW file that was 117Mb and in the Lr-Classic Library converted it to DNG- the result being a 53Mb file.

So your result 120>60 seems possible.

DNG conversion is always known to preserve the full image raw data, so I have no idea what other proprietary metadata may be getting deleted/re-arranged in the DNG file.

Regards. My System: Windows-11, Lightroom-Classic 15.1.1, Photoshop 27.3.1, ACR 18.1.1, Lightroom 9.0, Lr-iOS 10.4.0, Bridge 16.0.2 .

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