This operation interactively creates a mask based on a power spectrum which can be used for Fourier filtering. The operation solicits name of a power spectrum image which is displayed. It also solicits name of the output file which is in Fourier format. Using the mouse, user can create a mask on the power spectum space. Mask consists of circular Gaussians with values from 0...1.0. Up to 200 circles are allowed on each mask. The Gaussian circle sizes can be set with the initial menu and altered with the up-arrow and down-arrow keys while drawing masks. The final mask is saved to the output file only when the center mouse button is pushed to terminate the masking.
This operation replaces the old SPIDER 'GF operation for quasi-optical Fourier Filtration . It can be used to masks out Fourier coefficients from the input file in the vicinity of specified reflections, and transfers these coefficients into the output Fourier filter file. This filter file can then be multipled by a Fourier file for filtering.