The Auto Remove Gradient command can be used when the image has a bright background that varies linearly across the frame. Typical causes of gradients in astronomical images are sky-glow, moonlight and light pollution.
This problem can be reduced or even eliminated in many images by using this command. It estimates the background level in various regions of the image and then fits a bilinear equation to the background points. The resulting model is subtracted from the image, thus reducing the variations.
Note that the algorithm works best on star fields; images with a large foreground object consuming a significant part of the field can bias the background extraction.
Availability of this feature depends on Product Level.