Fix 3 failing Magick.NET unit tests
diff --git a/MagickCore/quantize.c b/MagickCore/quantize.c
index 3d5745f..0502c1d 100644
--- a/MagickCore/quantize.c
+++ b/MagickCore/quantize.c
@@ -653,7 +653,7 @@
       /*
         Monochrome image.
       */
-      intensity=GetPixelInfoLuma(image->colormap+0) > QuantumRange/2.0 ? 0.0 :
+      intensity=GetPixelInfoLuma(image->colormap+0) < QuantumRange/2.0 ? 0.0 :
         QuantumRange;
       if (image->colors > 1)
         {