Add HSI calculation

src/modules/colorPicker/ColorPickerUI/Helpers/ColorHelper.cs

@@ -52,6 +52,20 @@ namespace ColorPicker.Helpers
         internal static (double hue, double saturation, double brightness) ConvertToHSBColor(Color color)
             => (color.GetHue(), color.GetSaturation(), color.GetBrightness());
 
+        /// <summary>
+        /// Convert a given <see cref="Color"/> to a HSI color (hue, saturation, intensity)
+        /// </summary>
+        /// <param name="color">The <see cref="Color"/> to convert</param>
+        /// <returns>The hue [0°..360°], saturation [0..1] and intensity [0..1] of the converted color</returns>
+        internal static (double hue, double saturation, double intensity) ConvertToHSIColor(Color color)
+        {
+            var min = Math.Min(Math.Min(color.R, color.G), color.B) / 255d;
+
+            var intensity = 1d / 3d * (color.R + color.G + color.B);
+
+            return (color.GetHue(), intensity == 0d ? 0d : 1d - (min / intensity), intensity);
+        }
+
         /// <summary>
         /// Convert a given <see cref="Color"/> to a HSL color (hue, saturation, lightness)
         /// </summary>

src/modules/colorPicker/ColorPickerUI/Helpers/ColorRepresentationHelper.cs

@@ -27,6 +27,7 @@ namespace ColorPicker.Helpers
                 ColorRepresentationType.NCol => ColorToNCol(color),
                 ColorRepresentationType.HEX => ColorToHex(color),
                 ColorRepresentationType.HSB => ColorToHSB(color),
+                ColorRepresentationType.HSI => ColorToHSI(color),
                 ColorRepresentationType.HSL => ColorToHSL(color),
                 ColorRepresentationType.HSV => ColorToHSV(color),
                 ColorRepresentationType.HWB => ColorToHWB(color),
@@ -101,6 +102,24 @@ namespace ColorPicker.Helpers
                  + $", {brightnes.ToString(CultureInfo.InvariantCulture)}%)";
         }
 
+        /// <summary>
+        /// Return a <see cref="string"/> representation of a HSI color
+        /// </summary>
+        /// <param name="color">The <see cref="Color"/> for the HSI color presentation</param>
+        /// <returns>A <see cref="string"/> representation of a HSI color</returns>
+        private static string ColorToHSI(Color color)
+        {
+            var (hue, saturation, intensity) = ColorHelper.ConvertToHSIColor(color);
+
+            hue = Math.Round(hue);
+            saturation = Math.Round(saturation * 100);
+            intensity = Math.Round(intensity * 100);
+
+            return $"hsi({hue.ToString(CultureInfo.InvariantCulture)}"
+                 + $", {saturation.ToString(CultureInfo.InvariantCulture)}%"
+                 + $", {intensity.ToString(CultureInfo.InvariantCulture)}%)";
+        }
+
         /// <summary>
         /// Return a <see cref="string"/> representation of a HSL color
         /// </summary>