Today’s Question: I understand the exclamation point in Lightroom’s grid view (I think) but I thought that I should still be able to see a preview even if hard drive containing image was disconnected. Can you offer a solution?
Tim’s Quick Answer: Under “normal” circumstances you should indeed be able to see the thumbnails (and even the larger previews) for all of the images in your Lightroom catalog, even when the source images are not available. For any images for which a thumbnail or preview is not displayed, rendering new previews when the source images are available should solve the problem.
More Detail: Generally speaking, the previews for your photos are generated when the images are imported into your Lightroom catalog. I recommend using the “Standard” option for previews during the import process. If you have considerable free hard drive space you can also use the “1:1” option. As long as this process completes before you quit Lightroom (or disconnect an external hard drive) the previews will be available and visible whenever you have that catalog open in Lightroom.
When thumbnails and/or previews are not available for some of the images in your Lightroom catalog, you can simply render new previews for those images. You do need to have the images available for that process to work, which means you can’t have any images that display the exclamation point indicating the source file is not available.
So, for example, if all of your photos are stored on an external hard drive, you’ll first need to connect that hard drive. You could then select the images that need to have previews rendered, but in most cases I find it easier to simply select all photos within a folder that has some missing thumbnails or previews. You could navigate to a folder with some missing previews, then choose Edit > Select All from the menu (or press Ctrl+A on Windows or Command+A on Macintosh). Then, while in the Library module, choose Library > Previews > Build Standard-Sized Previews from the menu (if you prefer full resolution previews you can choose “Build 1:1 Previews” from that menu instead).
Lightroom will show you the progress of the preview rendering on the identity plate at the far left of the top panel. When that process is complete, all of the images you build previews for will have both thumbnails and previews visible even when the source images are not currently available.