I have an export option for a photo forum I post to, where the size limit is 200kb. I have set 200kb, 600x600 JPG as the export limits, and I routinely get files much bigger, memory-wise, than that, up to 260kb.
I can set the export dimension limit to 500x500, and still get files over 200kb. Today, after a file went to 260kb at 600x600, I set the dimension limit to 500x500, and the exported file size did not change: at 500x500, it was still a 260kb file. If I go through and tweak compression by hand, on every photo, or set a file size limit of 150kb, I can get under 200kb per file.
I've tried files where I set the limit from 200, to 190, to 180, to 170, and see no change in the exported file (still well over 200 in size), and then when I set it to 160 it jumps down to 150-160 in size. If the file was only 210kb on export with the 200kb limit, setting it to 180kb will generally get the file under 200kb.
Really, the file size limit does not do what it purports to do. It can clearly get the file below that size if I direct it by hand every time: I haven't specified anything that would artificially bulk the file up, like a quality setting that would be incompatible with the file size limit. It's free to compress the file as needed to meet the limit.
What I want it to do is meet the limit I set for it. I shouldn't have to dance around. I have this export setting for the express purpose of quickly producing under-200kb files, and I sort of expect Lightroom to manage it.
I've had this problem too, but it isn't the only one when creating small jpeg files from LR.
There is something seriously amiss in the export module. I also create a lot of 600 pixel wide/high files and not only are the file sizes far too high, but the quality is poor. I have two workarounds for this, both of which add a little time to the job, but make a big difference.
First is to export my files as full size jpegs (which I do anyway,) LR does a good job with these. Then get another programme to batch process these to give me the small sRGB files I also need!
Second is to use LR's web module and create a basic html site for a batch of images in a folder in a temp directory at the precise size I want. This has the advantage that I can add a watermark. Then just rename and move the folder containing the images from the web folder that has been created to where I want them, followed by deleting the rest of the web folder.
Working at low quality (38%) from the Export module gave me a file size for one image of 455KB. So then I told it to export at a max of 200KB, and it came out at 565KB. Using the web module with quality set at 70 gave a higher quality result and a file size of 105KB!
The problem seems to be worse on images where I've done quite a bit of work using local adjustments - rather as if they are actually performing these on the small jpeg and re-saving each time. Certainly something going very wrong - just like it was in LR2.x and I think it must be a logical error as presumably the web module uses the same library to create jpegs.
Small jpg's here are also not being constrained by 'limit file size to:' in LR3. Any word from Adobe?
No and there won't be, they're closed until 12th July, even then I wouldn't hold my breath for fix any time soon.
I can confirm the bug too. This is very bothersome and definitely should be fixed in the next point release. If a new feature is provided that allows users to explicitly limit the image size at export, it should never cross the limit, otherwise it's pretty useless. There are many online sites and marketplaces with a fixed limit on the image size. Hopefully a fix is in the works!
Just wanted to repost to this thread that, from my experience with 3.2, this bug is fixed. In several export sessions, no exported photo exceeded the export file size limit I specified. So thanks, Lightroom Team, for fixing this.
I've still had problems with the 3.2 release.
But there are two useful workarounds to get smaller file sizes with small jpegs using LR. One is to export a web site from LR - it seems to do a better job and removing unneeded metadata, and the other is to use the Jeremy Friedl's Metadata Wrangler plugin: http://regex.info/blog/lightroom-goodies/metadata-wrangler which is donation-ware and gives impressive control over metadata. Only took me 10 minutes to decide it was worth making a contribution.
The third way is to export big files and then reduce them in size in another program. I use ACDSee Pro (I got a free copy some years ago) as a file viewer but it very handily batch processes changing file size and seems to me to do a slightly better job than LR on quality/file size, though not enough for me usually to bother to use another piece of software.
I confirm that while size limit seems to now work, you loose some metadata, like date of shooting.
I had the problem when participating to a forum where date of shooting was mandatory : if I do not use size limit, it is OK but cumbersome to find the right settings (300K limit); if I use size limit it works but the image was refused because the date of shooting was somehow lost in the reduction (while other EXIF data are kept).
I think there is definitely a bug there. LR3 is a wonderful software but this kind of inconvenience can be rather annoying when posting on the web...
Try Friedl's Metadata Wranger plugin and see if that helps. It massages the metadata near the end of the processing, so you might end up with a slightly larger than expected image, but it might contain what you want. You can set it to have the minimal amount of metadata which should keep things in check.