ThresholdPreview  550 Magick++/lib/Magick++/Include.h   using MagickCore::ThresholdPreview;
ThresholdPreview 2453 magick/effect.c       case ThresholdPreview:
ThresholdPreview 1452 magick/option.c     { "Threshold", ThresholdPreview, UndefinedOptionFlag, MagickFalse },