Controlling JPEG file sizes in Lightroom 3

Lightroom JPEG export options

Summary: file sizes of low-resolution JPEGs that you export using Lightroom can be excessive if you don’t take steps to control the embedded metadata. The large file sizes can affect your site’s loading speed and that in turn can now affect your Google search rank.
Earlier this week, I was catching up on some well written and informative articles by London photographer and writer Peter Marshall when I came across this one mentioning the release of Lightroom 3.2RC; in the piece, Peter mentioned that he’d found Lightroom 3 to be generating relatively low quality JPEG files for a given file size, at the 600-pixel dimensions that he uses for his site.

Peter had noticed two significant things: first, that he was getting better JPEGs at any given file size when he created them using Lightroom’s web module (which is designed to export a complete web site) instead of the usual JPEG export method; second, that the problem was worse when he was exporting JPEGs of images for which he’d made use of Lightroom’s local adjustments, meaning brushes and graduated filters.

It turned out (see his follow-up post here, and the comments that follow it) that the metadata associated with the file was causing the bump in file size. Clicking “Minimize Embedded Metadata” when exporting JPEGs helps; installing a copy of Jeffrey Friedl’s Metadata Wrangler plugin for Lightroom 3 fixes the problem completely and has added benefits: you can set up presets that get saved with Lightroom’s own export presets. That means you can build a one-click Lightroom export preset that generates the right picture size for your site with all but the unimportant metadata removed, and just the important stuff retained. (Presets are the key to working quickly within Lightroom and are probably its most overlooked feature.)

Above: the checkbox used during export to minimise metadata. Not as effective as Jeffrey’s Metadata Wrangler.

Explanation: all local brush and graduated filter adjustments that you apply in Lightroom become part of an images’s metadata and are included on export, bumping up the size of the final JPEG file—particularly noticeable for small JPEGs, because this metadata size is a constant and can easily double the size of a file. Not a huge problem if you’re hosting one or two images on a page but if you’re putting up many, the extra file size is significant. For blogs that have the usual rolling front page, hosting all images from the last ten or twenty posts, this sort of thing can make a big difference for your visitors… and for Google.

Important for your photography site’s Google rank

These days, your site’s Google rank is partly dependent on the speed at which your site loads—see this important article from Google on the subject. It’s well worth doing what Peter is doing, optimising carefully and minimising JPEG image size. (On which note, if you’re using WordPress software and your own hosting account to manage your site’s content, you should make every attempt to install and enable WP Super Cache to speed up your site’s response under load. This isn’t the appropriate place to discuss the technical aspects of that plugin but it does its job very well. Obviously, make complete site backups first.)

Above: JPEG file sizes before and after reducing metadata in different ways. No affect on image quality.

Photo forum

As Peter mentions, we met at a monthly London event called Photo Forum where photographers (mostly photojournalists) show and discuss their work. The two of us here at Shoot Raw have been three or four times and always enjoyed it. It’s a busy event but a good way to see work that might be new to you and to meet other photographers, established and upcoming. (At the time of writing, the next event is on 9th September 2010.) It’s a credit to Jacobs Professional Services that they host the event every month.

Friedl on JPEG quality versus size in Lightroom

Jeffrey’s definitive article on Lightroom 3’s JPEG quality made the rounds a while back. If you haven’t read it and you generate JPEGs from Lightroom, pay a visit. It’s the last word on Lightroom 3’s JPEG quality versus file size and even those of us who thought we knew exactly what Lightroom was doing in this area learned a few things.

The metadata

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