radius = lastRadius[filterType]<=0 ? 2 : lastRadius[filterType];
gd.addNumericField("Radius", radius, 1, 6, "pixels");
int digits = imp.getType() == ImagePlus.GRAY32 ? 2 : 0;
if (filterType==OUTLIERS) {
gd.addNumericField("Threshold", lastThreshold, digits);
gd.addChoice("Which outliers", outlierStrings, outlierStrings[lastWhichOutliers]);
gd.addHelp(IJ.URL+"/docs/menus/process.html#outliers");
} else if (filterType==REMOVE_NAN)
gd.addHelp(IJ.URL+"/docs/menus/process.html#nans");
gd.addPreviewCheckbox(pfr); //passing pfr makes the filter ready for preview
gd.addDialogListener(this); //the DialogItemChanged method will be called on user input