Single-click in the list of filters to select the current filter to be applied to the data; in some cases there will be further parameters to select.
Pressing the Apply button or the a hot key will apply the current filter to the ORIGINAL image data. Double-clicking in the filter list is the same as pressing the Apply button.
Pressing the More button or the b hot key will apply the filter to the CURRENT image data, as modified by previous filter operations.
Pressing the Reset button, applying a filter to a different section, closing the window with Done, or flipping the data volume will all restore the original image data for a section, unless you press the Save button. Save will permanently replace the image data in memory with the processed data.
To do an FFT of a subregion, turn on Use Zap window subarea. If the rubber band is on in the active Zap window, the FFT will be taken of the area inside the rubber band. Otherwise, the area used will be the portion of the image showing in the window.
The Compute frequency button can be used to determine the frequency at a particular location in the FFT. First, click on that location with the first mouse button, or deposit a model point there, then press the button. If you are in model mode and there is a current model point, its position will be used; otherwise the current image position is used. The current image position is rounded to the nearest pixel while a model point can provide subpixel accuracy if needed. The program will compute the frequency in reciprocal pixels then divide by the pixel size in the model header to get the frequency that is show (e.g., reciprocal nanometers). The inverse of this value is also shown to provide a resolution value in real space units.
The panel also shows the scale that is used to convert from pixels in the FFT to frequency units.
The Edge Stopping Function radio buttons allow you to choose between the Rational edge stopping function and the Tukey biweight stopping function, which correspond to options -cc 2 and -cc 3, respectively, in Clip. The Tukey biweight will preserve more local structure than the rational edge stopping function.
The Iterations value controls how many iterations are run when Apply or More is pressed. The total number of iterations done is also reported. The routine will give the identical result if a certain number of iterations are done with multiple steps using More rather than all at once.
The K entry sets a threshold for the edge stopping function; when the number is too low virtually nothing will happen. The rational edge function may require smaller values than the Tukey biweight. The unscaled value is the number that should be specified with the -k option in Clip to achieve the same filtering on the raw data from the image file as is seen on the scaled byte data in 3dmod.
The Lambda value controls the so-called time-step; if images become noisier this probably needs to be reduced.