ThresholdPreview  404 Magick++/lib/Magick++/Include.h   using MagickCore::ThresholdPreview;
ThresholdPreview 3146 magick/effect.c       case ThresholdPreview:
ThresholdPreview 1398 magick/option.c     { "Threshold", (ssize_t) ThresholdPreview, MagickFalse },