The Spot Removal tool can be used to quickly remove spots or small blemishes from images. In addition to spot removal, it also has an option to remove sensor dust. Although the operation using a circular cursor to retouch each imperfection is the same between the Spot and Dust modes, those two adopt different algorithms so the final results will vary. Whereas the Spot option analyzes texture, color, and brightness from the sampled area and merges that with its immediate surroundings, the Dust mode estimates the light lost and compensates with a localized exposure adjustment. It is recommended, therefore, to limit each to their intended use.
Sensor dust can be commonly seen in similar or identical locations on images from one session. Dust can settle in the front of the so-called "filter-stack" of an image sensor and may appear in varying degrees of sharpness from image-to-image, depending on the aperture selected during capture. To save time when retouching dust spots from multiple images, use the Global Copy and Apply buttons to apply the corrections. Alternatively, make a local copy of the dust spots using the Adjustments Clipboard and apply the Dust setting to the rest of the images. Always check image files when automatically removing dust spots. The Spot Removal tool works with offline images so you can continue working on a Catalog without the source files available, for example, when you are away from the office and do not have access to an external drive or NAS. You can use multiple overlapping selections (up to 100 selections can be made per image), however, the brush-based Heal tool is recommended when more advanced retouching is required.