From acf6ddd7d9a48591de4ade57ff14111faafdbd65 Mon Sep 17 00:00:00 2001
From: Cristy <urban-warrior@imagemagick.org>
Date: Wed, 14 May 2025 19:23:30 -0400
Subject: [PATCH] correct NCC metric

---
 MagickCore/compare.c | 19 ++++++++++++-------
 MagickWand/compare.c | 14 +++++++++-----
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/MagickCore/compare.c b/MagickCore/compare.c
index c6fcb8b94b..e73f3860c7 100644
--- a/MagickCore/compare.c
+++ b/MagickCore/compare.c
@@ -457,10 +457,10 @@ static MagickBooleanType GetAbsoluteDistortion(const Image *image,
         else
           delta=QuantumScale*(Sa*(double) p[i]-Da*(double) GetPixelChannel(
             reconstruct_image,channel,q));
-        if ((QuantumRange*delta*delta) >= fuzz)
+        if ((delta*delta) >= fuzz)
           {
-            channel_distortion[i]+=fabs(delta);
-            channel_distortion[CompositePixelChannel]+=fabs(delta);
+            channel_distortion[i]++;
+            channel_distortion[CompositePixelChannel]++;
           }
       }
       channel_area++;
@@ -792,7 +792,8 @@ static MagickBooleanType GetMeanErrorPerPixel(Image *image,
 
   double
     area = 0.0,
-    maximum_error = MagickMinimumValue;
+    maximum_error = MagickMinimumValue,
+    mean_error = 0.0;
 
   MagickBooleanType
     status = MagickTrue;
@@ -821,7 +822,8 @@ static MagickBooleanType GetMeanErrorPerPixel(Image *image,
     double
       channel_area = 0.0,
       channel_distortion[MaxPixelChannels+1] = { 0.0 },
-      channel_maximum_error = MagickMinimumValue;
+      channel_maximum_error = MagickMinimumValue,
+      channel_mean_error = 0.0;
 
     ssize_t
       x;
@@ -873,6 +875,7 @@ static MagickBooleanType GetMeanErrorPerPixel(Image *image,
             GetPixelChannel(reconstruct_image,channel,q));
         channel_distortion[i]+=distance;
         channel_distortion[CompositePixelChannel]+=distance;
+        channel_mean_error+=distance*distance;
         if (distance > channel_maximum_error)
           channel_maximum_error=distance;
       }
@@ -901,6 +904,7 @@ static MagickBooleanType GetMeanErrorPerPixel(Image *image,
       }
       distortion[CompositePixelChannel]+=
         channel_distortion[CompositePixelChannel];
+      mean_error+=channel_mean_error;
       maximum_error+=channel_maximum_error;
     }
   }
@@ -920,8 +924,9 @@ static MagickBooleanType GetMeanErrorPerPixel(Image *image,
   }
   distortion[CompositePixelChannel]*=area;
   distortion[CompositePixelChannel]/=(double) GetImageChannels(image);
-  image->error.mean_error_per_pixel=distortion[CompositePixelChannel];
-  image->error.normalized_mean_error=distortion[CompositePixelChannel];
+  image->error.mean_error_per_pixel=QuantumRange*
+    distortion[CompositePixelChannel];
+  image->error.normalized_mean_error=mean_error;
   image->error.normalized_maximum_error=maximum_error;
   return(status);
 }
diff --git a/MagickWand/compare.c b/MagickWand/compare.c
index be73a52237..9ad698958a 100644
--- a/MagickWand/compare.c
+++ b/MagickWand/compare.c
@@ -1309,8 +1309,12 @@ WandExport MagickBooleanType CompareImagesCommand(ImageInfo *image_info,
       break;
     }
     case NormalizedCrossCorrelationErrorMetric:
-    case PhaseCorrelationErrorMetric:
     case StructuralDissimilarityErrorMetric:
+    {
+      similarity_metric=1.0-similarity_metric;
+      break;
+    }
+    case PhaseCorrelationErrorMetric:
     case UndefinedErrorMetric:
     {
       distortion=1.0-distortion;
@@ -1342,9 +1346,9 @@ WandExport MagickBooleanType CompareImagesCommand(ImageInfo *image_info,
             case MeanErrorPerPixelErrorMetric:
             {
               (void) FormatLocaleFile(stderr,"%.*g (%.*g, %.*g)",
-                GetMagickPrecision(),QuantumRange*distortion,
-                GetMagickPrecision(),image->error.normalized_mean_error,
-                GetMagickPrecision(),image->error.normalized_maximum_error);
+                GetMagickPrecision(),scale*distortion,
+                GetMagickPrecision(),distortion,GetMagickPrecision(),
+                image->error.normalized_maximum_error);
               break;
             }
             default:
@@ -1519,7 +1523,7 @@ WandExport MagickBooleanType CompareImagesCommand(ImageInfo *image_info,
             {
               (void) FormatLocaleFile(stderr,"    %.*g (%.*g, %.*g)\n",
                 GetMagickPrecision(),channel_distortion[MaxPixelChannels],
-                GetMagickPrecision(),image->error.normalized_mean_error,
+                GetMagickPrecision(),channel_distortion[MaxPixelChannels],
                 GetMagickPrecision(),image->error.normalized_maximum_error);
               break;
             }