OOF: Finite Element Analysis of Microstructures
Active areas are portions of the image to which all subsequent operations will be restricted. For example, if one portion of a mesh needs some extra refinement, you can define an active area that includes only that portion of the mesh. Or if you want to use the Demography tool to select pixels of a certain color only in one corner of an image, you can make just that corner active.
Initially, the entire image is active. Active areas are defined by specifying sets of pixels and using the /active_area/set menu. The current active area can be modified with /active_area/reduce and /active_area/expand. The whole image can be made temporarily active with /active_area/override.
When a subset of the image is active, the inactive parts are drawn faintly.