use an enum instead of ushort for IccParamtricCurve.Type

src/ImageSharp/MetaData/Profiles/ICC/Curves/IccParametricCurve.cs

@@ -12,7 +12,7 @@
         /// </summary>
         /// <param name="g">G curve parameter</param>
         public IccParametricCurve(double g)
-            : this(0, g, 0, 0, 0, 0, 0, 0)
+            : this(IccParametricCurveType.Type1, g, 0, 0, 0, 0, 0, 0)
         {
         }
 
@@ -23,7 +23,7 @@
         /// <param name="a">A curve parameter</param>
         /// <param name="b">B curve parameter</param>
         public IccParametricCurve(double g, double a, double b)
-            : this(1, g, a, b, 0, 0, 0, 0)
+            : this(IccParametricCurveType.Cie122_1996, g, a, b, 0, 0, 0, 0)
         {
         }
 
@@ -35,7 +35,7 @@
         /// <param name="b">B curve parameter</param>
         /// <param name="c">C curve parameter</param>
         public IccParametricCurve(double g, double a, double b, double c)
-            : this(2, g, a, b, c, 0, 0, 0)
+            : this(IccParametricCurveType.Iec61966_3, g, a, b, c, 0, 0, 0)
         {
         }
 
@@ -48,7 +48,7 @@
         /// <param name="c">C curve parameter</param>
         /// <param name="d">D curve parameter</param>
         public IccParametricCurve(double g, double a, double b, double c, double d)
-            : this(3, g, a, b, c, d, 0, 0)
+            : this(IccParametricCurveType.SRgb, g, a, b, c, d, 0, 0)
         {
         }
 
@@ -63,14 +63,12 @@
         /// <param name="e">E curve parameter</param>
         /// <param name="f">F curve parameter</param>
         public IccParametricCurve(double g, double a, double b, double c, double d, double e, double f)
-            : this(4, g, a, b, c, d, e, f)
+            : this(IccParametricCurveType.Type5, g, a, b, c, d, e, f)
         {
         }
 
-        private IccParametricCurve(ushort type, double g, double a, double b, double c, double d, double e, double f)
+        private IccParametricCurve(IccParametricCurveType type, double g, double a, double b, double c, double d, double e, double f)
         {
-            Guard.MustBeBetweenOrEqualTo(type, 0, 4, nameof(type));
-
             this.Type = type;
             this.G = g;
             this.A = a;
@@ -84,7 +82,7 @@
         /// <summary>
         /// Gets the type of this curve
         /// </summary>
-        public ushort Type { get; }
+        public IccParametricCurveType Type { get; }
 
         /// <summary>
         /// Gets the G curve parameter

src/ImageSharp/MetaData/Profiles/ICC/Enums/IccParametricCurveType.cs

@@ -0,0 +1,46 @@
+// <copyright file="IccClutDataType.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp
+{
+    /// <summary>
+    /// Formula curve segment type
+    /// </summary>
+    internal enum IccParametricCurveType : ushort
+    {
+        /// <summary>
+        /// Type 1: Y = X^g
+        /// </summary>
+        Type1 = 0,
+
+        /// <summary>
+        /// CIE 122-1996:
+        /// <para>For X &gt;= -b/a: Y =(a * X + b)^g</para>
+        /// <para>For X $lt; -b/a: Y = 0</para>
+        /// </summary>
+        Cie122_1996 = 1,
+
+        /// <summary>
+        /// IEC 61966-3:
+        /// <para>For X &gt;= -b/a: Y =(a * X + b)^g + c</para>
+        /// <para>For X $lt; -b/a: Y = c</para>
+        /// </summary>
+        Iec61966_3 = 2,
+
+        /// <summary>
+        /// IEC 61966-2-1 (sRGB):
+        /// <para>For X &gt;= d: Y =(a * X + b)^g</para>
+        /// <para>For X $lt; d: Y = c * X</para>
+        /// </summary>
+        SRgb = 3,
+
+        /// <summary>
+        /// Type 5:
+        /// <para>For X &gt;= d: Y =(a * X + b)^g + c</para>
+        /// <para>For X $lt; d: Y = c * X + f</para>
+        /// </summary>
+        Type5 = 4,
+    }
+}

src/ImageSharp/MetaData/Profiles/ICC/IccDataWriter.cs

@@ -1711,31 +1711,32 @@ namespace ImageSharp
         /// <returns>The number of bytes written</returns>
         public int WriteParametricCurve(IccParametricCurve value)
         {
-            int count = this.WriteUInt16(value.Type);
+            ushort typeValue = (ushort)value.Type;
+            int count = this.WriteUInt16(typeValue);
             count += this.WriteEmpty(2);
 
-            if (value.Type >= 0 && value.Type <= 4)
+            if (typeValue >= 0 && typeValue <= 4)
             {
                 count += this.WriteFix16(value.G);
             }
 
-            if (value.Type > 0 && value.Type <= 4)
+            if (typeValue > 0 && typeValue <= 4)
             {
                 count += this.WriteFix16(value.A);
                 count += this.WriteFix16(value.B);
             }
 
-            if (value.Type > 1 && value.Type <= 4)
+            if (typeValue > 1 && typeValue <= 4)
             {
                 count += this.WriteFix16(value.C);
             }
 
-            if (value.Type > 2 && value.Type <= 4)
+            if (typeValue > 2 && typeValue <= 4)
             {
                 count += this.WriteFix16(value.D);
             }
 
-            if (value.Type == 4)
+            if (typeValue == 4)
             {
                 count += this.WriteFix16(value.E);
                 count += this.WriteFix16(value.F);