https://github.com/ImageMagick/ImageMagick/issues/1610

diff --git a/MagickCore/pixel-accessor.h b/MagickCore/pixel-accessor.h
index 8af0e369cfbbd48aaa0c5cff8c56dc118e5859f0..56fba6c9784c122fc5079f95ba68e0569c7a0fc1 100644 (file)
--- a/MagickCore/pixel-accessor.h
+++ b/MagickCore/pixel-accessor.h
@@ -111,7 +111,7 @@ static inline PixelTrait GetPixelCbTraits(const Image *magick_restrict image)
 static inline Quantum GetPixelChannel(const Image *magick_restrict image,
   const PixelChannel channel,const Quantum *magick_restrict pixel)
 {
-  if (image->channel_map[channel].traits == UndefinedPixelTrait)
+  if (image->channel_map[image->channel_map[channel].offset].traits == UndefinedPixelTrait)
     return((Quantum) 0);
   return(pixel[image->channel_map[channel].offset]);
 }