Jeffrey Friedl, author of our favorite Lightroom export plug-in (for Smugmug), has developed a remarkable online-learning page on the topic of JPEG quality. The context is specific to Adobe Lightroom, but if you spend a bit of time with his “Sunset and Bird” Quality-Inspector you will see what I mean. E.g.,
(…) Quality-Inspector Features
In visually comparing one quality level to another, it’s very helpful to swap back and forth quickly between the two samples, as it hyper-highlights differences, revealing details of the difference that one would never otherwise notice. While this is useful, it’s important to maintain a sense of perspective about what viewers will eventually see and actually notice on their own. Don’t let yourself get carried away by raw pixel-peeping alone.
Comparing quality levels:
Comparing adjacent quality levels — Comparing adjacent quality levels is as simple as panning the mouse back and forth between the adjacent quality buttons.
Comparing a quality level versus perfect — Bringing the mouse just below a button reverts the display to the “lossless” perfect-quality version, so sweeping the mouse up and down into the button then below it toggles between the view for that button and the perfect-quality version.
Comparing any two quality levels — Selecting the small circular checkbox below a quality button makes that button the one reverted to when the mouse is brought under a button, so you can select the checkbox for one quality, then move to the button for the other and pan up and down to toggle between the views.
Read more » I can almost guarantee you will be surprised and rewarded.
NOTE: Jeff is developing (may have already released) a Lightroom plug-in similar to what you see on the linked web page. So you can evaluate the appropriate JPEG compression for your own specific images.