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Last week when exporting from LR with quality set at 100 and pixels per inch at 300 a file would export around 25-28 MB, today when exporting I noticed the file sizes are much smaller with the exact same settings (saving them around 7 to 8 MB). Wondering if I have inadvertently changed a setting? No other file size boxes are checked. Thank you!

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    \$\begingroup\$ Please show us your export settings. Otherwise we can just speculate. \$\endgroup\$
    – Romeo Ninov
    Commented Feb 13 at 18:03
  • \$\begingroup\$ Pixels per inch (ppi) setting is totally irrelevant to image file size. The number of pixels is a dimensionless number. \$\endgroup\$
    – Michael C
    Commented Feb 14 at 13:53
  • \$\begingroup\$ Are the images from the same camera? Have some of them been cropped or are they all the same number of pixels? Are the contents of the scene similar? Are they shot at the same ISO? (Noisier images of the same scene will produce larger files.) \$\endgroup\$
    – Michael C
    Commented Feb 14 at 13:55
  • \$\begingroup\$ In the export dialog box there is a setting for maximum file size. You may have that checked and set to 8MB or so. The loss of quality is invisible to my eye and it makes emailing the photos much easier. \$\endgroup\$
    – Ross Millikan
    Commented Feb 24 at 0:18

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The size of the output file is very dependent on content. Blurry images or images with somewhat uniform areas produce significantly smaller files.

Also, check the chroma sub-sampling setting if it is distinct from the quality setting. A quartered chroma can produce a file which is half the size of the full-chroma version for the same quality.

Note: Q100 is not a good idea, because your image is still subject to computations and round off. If you want to save the exact image, use another format (TIFF with LZW for instance), or if you accept the errors due to the DCT computations, use Q97, you will already significantly reduce the file size without losing much in accuracy.

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  • \$\begingroup\$ There are no chroma sub-sampling options in LR. \$\endgroup\$
    – Steven Kersting
    Commented Feb 14 at 14:28

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