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J
Julia21783527rnai
Participant
November 24, 2023
Question

Exploding file size of JPG after export out of Lightroom

  • November 24, 2023
  • 2 replies
  • 684 views

Dear community,


I would like to know why an image/JPG, which has, for example, a file size of just under 2MB and a resolution of 7000 x 4700 px before being imported to Lightroom has a significantly larger file size after export out of Lightroom..


For example, a JPG file is imported that is just under 2 MB in size with a resolution of 7000 x 4700 px.
This file is viewed in Lightroom and exported again unprocessed, the resolution is reduced to 6000x4700px and 300dpi.
A compression of 92% results in a file of about 5MB, at 100% it is just over 9MB.
The image is therefore significantly larger in terms of data volume after export, even though the resolution has been reduced and nothing else has been edited. This is just an example. If I edit an image, perhaps change the grain, the file size increases even more. I would be happy to attach screenshots of the export settings.


I have now tried this with different versions of Lightroom on different computers and colleagues have also reported the same observations. I haven't found anything about this in my research. It also has nothing to do with using a specific Lightroom version. The phenomenon exists since I use Lightroom for some years now, regardless of the type of version and operating system.

So I'm wondering, what the reason for this could be.

Unfortunately, Adobe support has not been helpful so far, so I'm trying my luck here.
Any suggestions?
    This topic has been closed for replies.

    2 replies

    D Fosse
    Community Expert
    D FosseCommunity Expert
    Community Expert
    November 24, 2023

    If a 7000 x 4700 file comes in at 2MB, then either the jpeg compression is very aggressive (low quality setting), or the image is almost featureless with little or no detail. Yes, that last bit matters.

     

    There are a few things you need to know about jpeg. It can shrink a file down to as little as 2-5% of its native full size, without very much immediately visible degradation. But it is always there, and with repeated saving it accumulates. This has nothing to do with resolution, it's just packaging the data. That packaging discards some data and rearranges some in a way that can't be fully reversed. Save it 4 or 5 times, and it starts to disintegrate.

     

    With all the drawbacks, the only reason jpeg has survived is that the compression is incredibly effective.

     

    Image content matters. The jpeg algorithm is much more effective on smooth and flat areas than it is on busy high frequency detail. These two are the same pixel size and the same jpeg compression level. The first  is 293 kB, the second 46 kB:

    J
    Julia21783527rnaiAuthor
    Participant
    November 24, 2023

    The image material must have been compressed quite aggressively, because there is a lot of details. OK, so that means that although I got a very highly compressed image in high resolution, as soon as I import this image into Lightroom and edit it or not, the original information is still there. And therefore the file size increases again when I export it at 100% or 92%, right?

    J
    Julia21783527rnaiAuthor
    Participant
    November 24, 2023

    Once a jpeg is opened, it is decompressed back to its full native size, which can be, say, 50 times bigger or more. And then when you re-export or re-save, the compression algorithm kicks in again. So every time it's compressed from scratch. Past sizes are irrelevant.

     

    What is relevant is that every time it's opened and decompressed, it doesn't fully return to the previous state. Something is lost in the compression, and it accumulates.

     

    Which is why a jpeg should always be considered a one-off final delivery end product. It's easy to think that if you just stay at "maximum quality", you'll be fine. But in fact there is no such thing as maximum quality with jpeg and the term is misleading. There is always degradation, just less. But it's there.

     

    Lightroom's handling of jpeg is parametric, meaning that the file isn't resaved while working. Only the instructions for processing are. So you're safe while working in Lightroom - but at one point you have to output.


    Ok, thank you for the explanation!

    dj_paige
    dj_paige
    Legend
    November 24, 2023

    Exporting at quality 100 will cause the exported file to expand. Usually quality 100 is not needed, and a quality in the 70-80 range will suffice for most purposes. A quality in the 70-80 range will be visually indistinguishable from quality 100, but much smaller file size.

     

    Please read: http://regex.info/blog/lightroom-goodies/jpeg-quality

    J
    Julia21783527rnaiAuthor
    Participant
    November 24, 2023

    Thank you! Very interesting that Lightroom actually only has 13 quality levels within 1-100.
    In this example, a photographer has sent an already edited and, above all, very heavily compressed image. Normally the file size at a resolution of 7000x4700px is well over 2 MB. That's why I don't want to compress such an image even more. I don't know how a customer will use it in the end. And that's why the 100% or 92%. However, I am surprised that the file size increases, although the resolution is reduced to 6000x4000px during export. That shouldn't happen, right?

    dj_paige
    dj_paige
    Legend
    November 24, 2023

    That shouldn't happen, right?

     

    Wrong.

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