Quick Lightroom Tip: Regenerate Previews after you've finished with a project
Here's a very quick Lightroom tip for you. One of the frustrating things about the way Lightroom's preview system works is that it only generates previews when you tell it to, usually upon import. As soon as you make any changes to an image, the preview for that image is lost. In order to make sure you can keep browsing through your library speedily, it's important to periodically re-build previews.
Previews are essential to the way the Library works in Lightroom. They are a pre-rendered jpeg version of your images, which allows Lightroom to quickly load a view of your photo when you go to it. In this case I'm just talking about standard previews. When you generate standard previews, Lightroom renders a Jpeg of your raw file, usually at screen res (the settings are in the preferences). When you move from image to image, the photo will load instantly, because it's loading the preview, rather than trying to render the raw file with all your changes each time. However, if you don't have a preview generated for a particular image, Lightroom will display the loading badge for a few seconds while it builds a temporary preview. This temporary preview is cached but only for a short time. If you go back to the same image later it may have to load again just to view it.
This becomes a problem when you edit images. Say you're working on a folder full of images from a recent shoot, for example. When you first import the images, you probably have told Lightroom to generate previews. Once the previews are generated, you should be able to quickly browse through the images with little delay in the Library. However, once you start making edits, you may find that Lightroom has to now stop and load a preview for the images that you edited. This is because Lightroom does not generate new previews after you edit an image. It stores a cached version but as i mentioned above this is only temporary. In order to address this you need to manually re-generate previews.
What I usually do once I'm finished on a project, is manually re-generate standard previews. You can do this by going to the Library module, select all the images in the project that you're currently working on, and then from the Library menu choose:
Previews > Build Standard Sized Previews
Once these are re-built you shouldn't have any loading issues in the Library again.
Why not 1:1 previews I hear you ask? Well, the reason that I don't re-generate 1:1 previews is two fold. Firstly it takes a lot of time, and secondly they take up a lot of space. You only need 1:1 previews for zooming in, and I usually only need to do that when a project is first imported and I'm checking focus. Usually when I re-generate previews it's so I can browse the library quicker, and 1:1 previews are not really necessary at this stage. That's just my workflow though.
I hope this little tip has been of help. One of the things I miss from Aperture was the way it handled previews. It would render previews in the background, and it would do it automatically whenever you made a change to an image, so you never had to really worry about it.
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