What are Photoshop Smart Filters?

To work with Smart Filters, you need to work with Smart Objects. When using Smart Objects, Photoshop stores a copy of the original pixels; so, if you make changes to the Smart Object’s appearance by transforming or applying a filter, the original pixel data is still available. If you transform again or change the filter settings, the new appearance is based on the original pixels.

For example, say that you create a Smart Object from a photo and you scale that Smart Object to 50%, is the image’s quality degraded? Yes, just as if you had scaled the original photo rather than a Smart Object. Now let’s say that you need to scale the image again, this time to 150% of the current size: Photoshop returns to the original pixel data and re-scales it to 75% rather than resampling the already-scaled appearance. Downsampling to 50% then upsampling to 150% will generally degrade an image significantly more than Downsampling once to 75%