Quality Settings When Exporting JPGs from Lightroom

The Lightroom export function allows you fine tune the quality of the resulting JPEGs in increments of single percentage points. But it turns out that the quality settings actually work in bands.

When you export JPG images from Lightroom you have a quality slider that goes from 0% to 100%. You can also manually type in a number for the quality setting. The feature allows you fine tune the quality in increments of one percent. So you’d think an image exported at 85% would be ever-so-slightly smaller and of less quality than one exported at 86%. It turns out that’s not the case.

I was just about to set up a new Lightroom export preset for a new online archive where I’d be using JPGs, and I wanted to settle on a JPG quality setting to use. For an archival / delivery use like this, I would typically use either 95% or 100%. I’ve often heard that there was no practical benefit to setting it at 100% but you do end up with much larger file sizes. And I’ve assumed that 95% keeps nearly all the quality benefits but reduces the filesize. But I thought I’d do a quick test to how much file size was really saved. The results surprised me.

I used a large original file (without any export resizing) taken with a D800 so that any size differences would be noticeable. The original file dimensions are 7360 x 4912 pixels. Because JPG compression works by clumping similar tones together, I wanted to use an image with a mix of colors, a range of shading, and a fair amount of detail. I used this image of a ship navigating through Antarctic sea ice.

I exported the file multiple times, each time only changing the quality setting and the corresponding filename. All of the other export options were kept exactly the same. The files were exported without any resizing, and no post-export changes were applied. Since I wouldn’t normally use a quality setting below 60%, I ran the test between 60% and 100%. Here’s what I got:

There are obviously some big differences in file sizes with different amounts of compression applied. But that’s expected. What I didn’t expect is that the increments are in bands rather than individual percentage points. An image exported at 93% is identical to an image exported at 100%. And an image exported at 69% percent results in a file exactly the same as one at a quality setting of 62% (assuming you haven’t changed any other export settings, of course).

Of course, you might point out that those filesizes in that screenshot are rounded to 100K, and that the differences might be smaller than that. But it turns out they’re not. Here’s the filesystem size down to the byte for the file exported at a quality setting of 85 and another at 92.

So the filesize is the same, I hear you say, but that doesn’t meant that the compression is the same. Good point.

Because there’s no real way to visually tell differences that small, I took subjective perception out of the equation by using software specifically designed to tell the differences between files (known as diff software – I used Kaleidoscope) on a byte-by-byte basis.

Here’s a side-by-size visual comparison of the 85% quality setting file (left) with the 92% quality setting file (right). Both are zoomed at 100% view. (If you click on the thumbnail it’ll open the screenshot at full size (although there’s an added layer of compression in making the JPG of the screenshot itself, of course…)).

There’s certainly no perceptual visual difference. So I let the diff software do its magic. The result was clean, confirming that the files are, pixel-for-pixel and byte-for-byte, identical.

For comparison, I ran the same test using the 85% version and the 93% version. Again, if there’s any visual difference it’s pretty much impossible to spot.

But in running the diff test, the results showed that the files are quite different this time.

So the takeaway is that rather than single-point fine-tuning, the JPG quality setting in Lightroom actually works in bands. Exporting a file at 93% quality setting is exactly the same as using 100%, and 85% is exactly the same as 92%, and so on. While you have a scale that goes from 0 to 100, in reality it’s much closer to the traditional JPG scale of 1 to 10.

Here are the bands for quality settings between 60% and 100%. Choosing a setting within a band will result in exactly the same file as another setting in that same band. All bands are inclusive (ie. the band 60-69 includes settings of 60 and 69).

60-69
70-76
77-84
85-92
93-100

Interestingly, saving the file with an sRGB colorspace resulted in a bigger file than exactly the same file and settings except in ProPhoto colorspace (19.2 MB vs 18.1 MB). Since ProPhoto is a much larger colorspace than sRGB and therefore allows for more individual colors, I expected the opposite. My guess is it has to do with the shapes of the colorspaces rather than their depths, and that therefore it will depend on the color tones in the image you’re exporting. But since filesize isn’t really a factor in choosing which colorspace to use, I haven’t investigated further.

I also haven’t tested other software to see if it does the same thing. So I don’t know if this is Lightroom-specific, Adobe-specific, or something to do with the original JPG compression algorithm itself.

Bonus Tip: Jeffrey Friedl has an interesting Lightroom plugin that allows you to export JPGs at each of Lightroom’s quality settings so that you can compare them side by side. You can find it here.

View Comments

  • I have a question regarding JPEG conversion in LR vs JPEG conversion in Photoshop. Hopefully you will be able to advise me on how to proceed.
    I see something peculiar when I export high res jpegs from LR catalogues/archives.
    I created a high res jpeg archive using Bridge/Photoshop action to save files as level 12 jpegs. These jpegs are useful since agencies and other clients will accept high res jpegs for publication.
    I have a LR catalogue for these jpegs. I then export selected jpegs from that archive for client consideration. I use the LR export feature @100%.

    However I have noticed that the file size for the LR exported jpegs is smaller than the file size for a jpeg generated directly from the tif via photoshop. It’s as if LR is not exporting a full sized High Res (level 12/100% jpeg) using the export feature.
    Example
    Tif to JPEG (via Bridge/PS action)- 10.25 Mb
    From LR Tif catalogue- Tif to JPEG- export- 9.71 Mb
    From LR JPEG archive- export JPEG- 9.77 Mb
    In both LR cases the LR export generates a smaller file that may not, therefore be level 12 jpeg. I suspect this because if I correct something in the exported jpeg file PS asks me to re-save as jpeg rather than simply saving the corrected file. As if the file was not originally a 100% jpeg.
    While I assume the exported LR jpegs to be 100% they seem in fact be smaller. For clients that could be an issue.
    Thoughts? Thanks!
    Don

  • This is clearly a flaw with Lightroom (and IMHO further evidence of their frequent lazy programming). Here are the file sizes results from exporting an image in CaptureOne
    jpeg 100 = 11.4mb
    jpeg 99 = 9.3mb
    jpeg 98 = 7.8mb
    jpeg 97 = 6.9mb
    jpeg 96 = 6.0mb
    jpeg 95 = 5.5mb
    jpeg 94 = 4.9mb
    jpeg 93 = 4.6mb
    jpeg 92 = 4.3mb
    jpeg 91 = 4.0mb
    jpeg 90 = 3.8mb
    jpeg 89 = 3.6mb

  • Hello David

    Thanks for your reply.
    The profile was Adobe Photo. I have just taken the image back to the original version and altered the colour manually and its fine now. It must have been the profile that was causing this.

    Thanks again

    Vincent

  • I have just exported a file from LR cc 100 percent Jpeg and it has lifted the colour saturation and vibrancy. How do I keep the same edited image when exporting?

    Many thanks

    Vincent

    • Did you change the color profile as well? Going from something like ProPhoto to sRGB can do what you describe and can be particularly noticeable, depending on the colors in the image and how much they might be bunched or clipped in the process. And there could be other factors, such as the way the viewing app deals with embedded color profiles, etc. To troubleshoot that part, you could export the image from Lightroom and then reimport it back in (apologies if that's what you're already doing). That at least will help narrow down whether it's something in the way that apps are displaying the images or something in the image itself. That is, some apps for viewing JPGs can juice the saturation and contrast. I know of issues with Firefox oversaturating colors, for example.

      • Still doing it. Every time I export it is enhancing the colours. Do Adobe have a live chat function or could I email them with this question?

        Sorry Im new to LR so a steep learning curve for me!

        Thanks

  • Thanks for this post. I did nearly the same analysis you did and was sure I was doing something wrong.

  • Hello. I renew my pc software (Windows), and after that, my dimensions of exported jpeg in LR 6.12 has fallen. For example, first time size was 14.6Mb and after that 13.4. I ask a friend of mine to put my raw in their LR, same version, and result is 19.7 (250dpi) and 16.9 (300dpi).

  • Interesting read, however i can clearly spot the difference in your sample images, its not the sharpness, but the colors. Colors on the lower quality image are much more saturated than they are on the higher one.

    • Yes, the higher compression blocks colors more at the expense of more tones and tends to favor saturated over subtle tones.

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