In past versions of Lightroom, it was not possible to make edits in the Develop module (nor the Quick Develop panel) to files that were off-line. In Lightroom 5, it is now possible to make these types of edits by creating Smart Previews for the images. Smart Previews are a new type of “preview” (not to be confused with the previews generated to view images in the Library module). They are significantly smaller than the original raw files and are stored in the same folder as your catalog (Smart Preview.lrdata”).
In order to create Smart Previews, the original files must be on-line. Therefore, you will want to make the Smart Previews before taking the images off-line. There are several ways to create Smart Previews in Lightroom:
• On Import – in the File Handling panel, check the option to “Build Smart Previews”.
• In the Library module – selecting your photos (or folders of photos) and select Library > Previews > Build Smart Previews (use this method to create Smart Previews for images that have already been imported into Lightroom).
• In Preferences – choose Preferences > General > Build Smart Previews on Import.
• When exporting as a Catalog – select File > Export as Catalog and check the option to “Build Smart Previews”.
If you have created Smart Previews for files, in the Develop module, the Histogram will notify you as to what you are working with:
• “Original” if there is not a smart preview built for the file and the original is on-line.
• “Original + Smart Preview” if there is a Smart Preview and the original is online.
• “Smart Preview” if there is a Smart Preview and the original is off-line.
When you make changes to a file that is off-line and has a Smart Preview, when the originals become available (are on-line), any changes there were made to the Smart Preview are automatically applied to the original. There is no action that you need to do – Lightroom will automatically apply all changes made to the Smart Preview to the original file. Basically, the rule is that if there is an original, then Lightroom will use the original, if the originals are not on-line, then Lightroom will use the Smart Preview. And of course if the original file is online, both the original and the Smart Preview are both updated as changes are made.
Keep in mind that these smart previews are smaller version of the original files (there are several reasons for this, the most obvious is to reduce the amount of space they take on the hard drive). With that said, since they are only 2540 pixels on the long edge, when applying Sharpening and Noise Reduction settings in the Details panel, the Smart Preview view at 100% will be a different magnification than the original. Therefore, for the most accuracy, you might need to confirm the setting when the files are on-line and you are able to view the original at 100%.
Finally, not only can use Smart Previews to Develop images when they’re off-line, you are also able to use them in the Publish Services panel (in case, for example, you want to publish your off-line files to Facebook or Flickr) and Export them as JPEG. You can even use them to layout a book (although you will not be able to print the book until the original images are on-line as the quality of the Smart Previews will not be high enough to print), and create and output a video slideshow (although again, they can not be used to output a slideshow to PDF because of quality concerns) and create and export web galleries. The best rule of thumb; for the highest quality, you’ll most likely want your original files when outputting files.