Today’s Question: Are there any limitations or downsides to editing a Smart Preview in Lightroom Classic? I am thinking in particular of brush mask edge resolution differences that might exist between a mask created within a Smart Preview versus the full resolution original image file, especially with the “Auto Mask” checkbox turned on.
Tim’s Quick Answer: The negative consequences of using Smart Previews in the Develop module within Lightroom Classic are very minor, and mostly relate to the fact that the overall image quality for the Smart Preview will not match the higher quality of the original image.
More Detail: Today’s question is a follow-up to my answer in the May 10th Ask Tim Grey eNewsletter regarding Smart Previews in Lightroom Classic. If you’d like to review the original question and answer, you can find them on the blog here:
In short, in Lightroom Classic you can build Smart Previews for photos, which enable you to perform various tasks with your photos even when the source image files are not available. That means an external hard drive that contains your photos could be disconnected, but you could still work in the Develop module or export reduced-resolution copies of the photos based on the Smart Previews. There’s also an option in Preferences to prioritize the use of Smart Previews in the Develop module even when the source photos are available, in order to improve performance.
The primary disadvantage to working with Smart Previews is that those previews are a reduced-resolution version of the original image. Therefore, you aren’t seeing a top-quality preview for the photo as you’re making decisions about the adjustments you apply.
This is a very minor issue that really won’t have a significant impact on the final image quality, since the adjustments applied based on the Smart Preview will synchronize with the source image as soon as it is available again. So while in principle I prefer not to use Smart Previews in the Develop module, the negative consequences of doing so are very minor.
This holds true if you are applying targeted adjustments with the masking features, even if you are making use of the “Auto Mask” option for the Brush feature. The masks you create based on the Smart Preview will still be very accurate, and those masks will be scaled for the full-resolution image when the updates are synchronized.
Therefore, if you feel there is an advantage being able to use Smart Previews in the Develop module, then I would not try to discourage you from doing so. If you don’t need Smart Previews in your workflow then I wouldn’t suggest generating them, but the downside to using them is absolutely minimal.