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diff --git a/MagickCore/enhance.c b/MagickCore/enhance.c
index 853505162774a706150fcd22e961fc84e480fe5b..67bb1ca4772c6eba83c235407fb65719fa4af748 100644 (file)
--- a/MagickCore/enhance.c
+++ b/MagickCore/enhance.c
@@ -3356,10 +3356,11 @@ MagickExport MagickBooleanType SigmoidalContrastImage(Image *image,
   (Sigmoidal((a),(b),(x))-Sigmoidal((a),(b),0.0)) / \
   (Sigmoidal((a),(b),1.0)-Sigmoidal((a),(b),0.0)) )
   /*
-    Inverse of ScaledSigmoidal, used for +sigmoidal-contrast. In
-    HDRI, the argument of the hyperbolic tangent (resp. logistic
-    sigmoidal) may be outside of the interval (-1,1) (resp.
-    (0,1)), hence the branching.
+    Inverse of ScaledSigmoidal, used for +sigmoidal-contrast.
+    Because b may be 0 or 1, the argument of the hyperbolic tangent
+    (resp. logistic sigmoidal) may be outside of the interval (-1,1)
+    (resp. (0,1)), even when creating a LUT, hence the branching.
+    In addition, HDRI may have out of gamut values.
     InverseScaledSigmoidal is not a two-side inverse of
     ScaledSigmoidal: It is only a right inverse. This is unavoidable.
   */