Fix HSV/BGRA conversions.

Former-commit-id: 15347486e210642b35e35e1c3220d86778897773
Former-commit-id: ce3d10d48dc5149cb84ac3c6fb2d442c98d0950a
Former-commit-id: ed21c57a33d1f5da11052bb97746f0ebeb63597e

src/ImageProcessor/Colors/Hsv.cs

@@ -52,7 +52,7 @@ namespace ImageProcessor
         /// <remarks>A value ranging between 0 and 100.</remarks>
         /// </summary>
         public readonly float S;
-        
+
         /// <summary>
         /// Gets the V value (brightness) component.
         /// <remarks>A value ranging between 0 and 100.</remarks>
@@ -117,30 +117,33 @@ namespace ImageProcessor
         /// </returns>
         public static implicit operator Hsv(Bgra color)
         {
-            float max = Math.Max(color.R, Math.Max(color.G, color.B));
-            float min = Math.Min(color.R, Math.Min(color.G, color.B));
-            float delta = max - min;
-
-            if (Math.Abs(max) < Epsilon)
+            float r = color.R / 255f;
+            float g = color.G / 255f;
+            float b = color.B / 255f;
+
+            float max = Math.Max(r, Math.Max(g, b));
+            float min = Math.Min(r, Math.Min(g, b));
+            float chroma = max - min;
+            float h = 0;
+            float s = 0;
+            float v = max;
+
+            if (Math.Abs(chroma) < Epsilon)
             {
-                return new Hsv(0, 0, 0);
+                return new Hsv(0, s * 100, v * 100);
             }
 
-            float h = 0.0F;
-            float s;
-            float v;
-
-            if (Math.Abs(delta) < Epsilon) { h = 0; }
-            else if (Math.Abs(color.R - max) < Epsilon) { h = (color.G - color.B) / delta; }
-            else if (Math.Abs(color.G - max) < Epsilon) { h = 2 + (color.B - color.R) / delta; }
-            else if (Math.Abs(color.B - max) < Epsilon) { h = 4 + (color.R - color.G) / delta; }
+            if (Math.Abs(chroma) < Epsilon) { h = 0; }
+            else if (Math.Abs(r - max) < Epsilon) { h = (g - b) / chroma; }
+            else if (Math.Abs(g - max) < Epsilon) { h = 2 + (b - r) / chroma; }
+            else if (Math.Abs(b - max) < Epsilon) { h = 4 + (r - g) / chroma; }
 
             h *= 60;
             if (h < 0.0) { h += 360; }
 
-            s = delta / max;
-            v = max / 255F;
-            return new Hsv(h, s, v);
+            s = (chroma / v);
+
+            return new Hsv(h, s * 100, v * 100);
         }
 
         /// <summary>
@@ -155,9 +158,12 @@ namespace ImageProcessor
         /// </returns>
         public static implicit operator Bgra(Hsv color)
         {
-            if (Math.Abs(color.S) < Epsilon)
+            float s = color.S / 100;
+            float v = color.V / 100;
+
+            if (Math.Abs(s) < Epsilon)
             {
-                byte component = (byte)(color.V * 255);
+                byte component = (byte)(v * 255);
                 return new Bgra(component, component, component, 255);
             }
 
@@ -165,51 +171,51 @@ namespace ImageProcessor
             int i = (int)(Math.Truncate(h));
             float f = h - i;
 
-            float p = color.V * (1.0f - color.S);
-            float q = color.V * (1.0f - (color.S * f));
-            float t = color.V * (1.0f - (color.S * (1.0f - f)));
+            float p = v * (1.0f - s);
+            float q = v * (1.0f - (s * f));
+            float t = v * (1.0f - (s * (1.0f - f)));
 
             float r, g, b;
             switch (i)
             {
                 case 0:
-                    r = color.V;
+                    r = v;
                     g = t;
                     b = p;
                     break;
 
                 case 1:
                     r = q;
-                    g = color.V;
+                    g = v;
                     b = p;
                     break;
 
                 case 2:
                     r = p;
-                    g = color.V;
+                    g = v;
                     b = t;
                     break;
 
                 case 3:
                     r = p;
                     g = q;
-                    b = color.V;
+                    b = v;
                     break;
 
                 case 4:
                     r = t;
                     g = p;
-                    b = color.V;
+                    b = v;
                     break;
 
                 default:
-                    r = color.V;
+                    r = v;
                     g = p;
                     b = q;
                     break;
             }
 
-            return new Bgra((byte)b, (byte)g, (byte)r);
+            return new Bgra((byte)(Math.Round(b * 255)), (byte)(Math.Round(g * 255)), (byte)(Math.Round(r * 255)));
         }
 
         /// <summary>

tests/ImageProcessor.Tests/Colors/ColorConversionTests.cs

@@ -10,6 +10,7 @@
 
 namespace ImageProcessor.Tests
 {
+    using System;
     using System.Diagnostics.CodeAnalysis;
 
     using Xunit;
@@ -94,13 +95,21 @@ namespace ImageProcessor.Tests
             Justification = "Reviewed. Suppression is OK here.")]
         public void BgrToHsv()
         {
+            // Black
+            Bgra b = new Bgra(0, 0, 0, 255);
+            Hsv h = b;
+
+            Assert.Equal(0, h.H);
+            Assert.Equal(0, h.S);
+            Assert.Equal(0, h.V);
+
             // White
             Bgra color = new Bgra(255, 255, 255, 255);
             Hsv hsv = color;
 
             Assert.Equal(0, hsv.H);
             Assert.Equal(0, hsv.S);
-            Assert.Equal(1, hsv.V);
+            Assert.Equal(100, hsv.V);
 
             // Dark moderate pink.
             Bgra color2 = new Bgra(106, 64, 128, 255);
@@ -109,6 +118,51 @@ namespace ImageProcessor.Tests
             Assert.Equal(320.6, hsv2.H, 1);
             Assert.Equal(50, hsv2.S, 1);
             Assert.Equal(50.2, hsv2.V, 1);
+
+            // Ochre.
+            Bgra color3 = new Bgra(34, 119, 204, 255);
+            Hsv hsv3 = color3;
+
+            Assert.Equal(30, hsv3.H, 1);
+            Assert.Equal(83.3, hsv3.S, 1);
+            Assert.Equal(80, hsv3.V, 1);
+        }
+
+        [Fact]
+        public void HsvToBgr()
+        {
+            // Dark moderate pink.
+            Hsv hsv = new Hsv(320.6f, 50, 50.2f);
+            Bgra bgra = hsv;
+
+            Assert.Equal(bgra.B, 106);
+            Assert.Equal(bgra.G, 64);
+            Assert.Equal(bgra.R, 128);
+
+            // Ochre
+            Hsv hsv2 = new Hsv(30, 83.3f, 80);
+            Bgra bgra2 = hsv2;
+
+            Assert.Equal(bgra2.B, 34);
+            Assert.Equal(bgra2.G, 119);
+            Assert.Equal(bgra2.R, 204);
+
+            // White
+            Hsv hsv3 = new Hsv(0, 0, 100);
+            Bgra bgra3 = hsv3;
+
+            Assert.Equal(bgra3.B, 255);
+            Assert.Equal(bgra3.G, 255);
+            Assert.Equal(bgra3.R, 255);
+
+            // Check others.
+            Random random = new Random(0);
+            for (var i = 0; i < 1000; i++)
+            {
+                Bgra bgra4 = new Bgra((byte)random.Next(255), (byte)random.Next(255), (byte)random.Next(255));
+                Hsv hsb4 = bgra4;
+                Assert.Equal(bgra4, (Bgra)hsb4);
+            }
         }
     }
 }