Fixed some more code issues

HPPH/PixelHelper.Average.cs

@@ -56,7 +56,7 @@ public static partial class PixelHelper
         };
     }
 
-    internal static Generic3ByteData Average(ReadOnlySpan<Generic3ByteData> data)
+    private static Generic3ByteData Average(ReadOnlySpan<Generic3ByteData> data)
     {
         if (data == null) throw new ArgumentNullException(nameof(data));
         if (data.Length == 0) return default;
@@ -70,7 +70,7 @@ public static partial class PixelHelper
                                     (byte)(sum.L3 / count));
     }
 
-    internal static Generic4ByteData Average(ReadOnlySpan<Generic4ByteData> data)
+    private static Generic4ByteData Average(ReadOnlySpan<Generic4ByteData> data)
     {
         if (data == null) throw new ArgumentNullException(nameof(data));
         if (data.Length == 0) return default;

HPPH/PixelHelper.MinMax.cs

@@ -62,7 +62,7 @@ public static unsafe partial class PixelHelper
         };
     }
 
-    internal static Generic3ByteMinMax MinMax(ReadOnlySpan<Generic3ByteData> data)
+    private static Generic3ByteMinMax MinMax(ReadOnlySpan<Generic3ByteData> data)
     {
         byte minB1 = byte.MaxValue, minB2 = byte.MaxValue, minB3 = byte.MaxValue;
         byte maxB1 = byte.MinValue, maxB2 = byte.MinValue, maxB3 = byte.MinValue;
@@ -132,7 +132,7 @@ public static unsafe partial class PixelHelper
         return new Generic3ByteMinMax(minB1, maxB1, minB2, maxB2, minB3, maxB3);
     }
 
-    internal static Generic4ByteMinMax MinMax(ReadOnlySpan<Generic4ByteData> data)
+    private static Generic4ByteMinMax MinMax(ReadOnlySpan<Generic4ByteData> data)
     {
         byte minB1 = byte.MaxValue, minB2 = byte.MaxValue, minB3 = byte.MaxValue, minB4 = byte.MaxValue;
         byte maxB1 = byte.MinValue, maxB2 = byte.MinValue, maxB3 = byte.MinValue, maxB4 = byte.MinValue;

HPPH/PixelHelper.Sum.cs

@@ -64,7 +64,7 @@ public static unsafe partial class PixelHelper
         };
     }
 
-    internal static Generic4LongData Sum(ReadOnlySpan<Generic3ByteData> data)
+    private static Generic4LongData Sum(ReadOnlySpan<Generic3ByteData> data)
     {
         long b1Sum = 0, b2Sum = 0, b3Sum = 0;
 
@@ -180,7 +180,7 @@ public static unsafe partial class PixelHelper
         return new Generic4LongData(b1Sum, b2Sum, b3Sum, data.Length * 255);
     }
 
-    internal static Generic4LongData Sum(ReadOnlySpan<Generic4ByteData> data)
+    private static Generic4LongData Sum(ReadOnlySpan<Generic4ByteData> data)
     {
         long b1Sum, b2Sum, b3Sum, b4Sum;
         int i = 0;