Now tests match ColorMine.

Former-commit-id: c7d55f44c558d6d77df183a3e8bdc2c9a0fcc94a
Former-commit-id: 59d24dd0b4440b6067dc6630dc453b06fa70184d
Former-commit-id: 4d0025941b7d5617a8b5c8bebcb37cfec8f13415

src/ImageProcessor/Colors/ColorTransforms.cs

@@ -192,11 +192,16 @@ namespace ImageProcessor
             float y3 = y * y * y;
             float z3 = z * z * z;
 
-            y = (y3 > 0.008856F) ? y3 : (y - 16F / 116F) / 7.787F;
             x = (x3 > 0.008856F) ? x3 : (x - 16F / 116F) / 7.787F;
+            y = (cieLabColor.L > 0.008856F * 903.3F) ? y3 : (cieLabColor.L / 903.3F);
             z = (z3 > 0.008856F) ? z3 : (z - 16F / 116F) / 7.787F;
 
-            // Then XYZ to RGB
+            x *= 0.95047F;
+            //y *= 1F;
+            z *= 1.08883F;
+
+            // Then XYZ to RGB (multiplication by 100 was done above already)
+
             float r = (x * 3.2406F) + (y * -1.5372F) + (z * -0.4986F);
             float g = (x * -0.9689F) + (y * 1.8758F) + (z * 0.0415F);
             float b = (x * 0.0557F) + (y * -0.2040F) + (z * 1.0570F);

src/ImageProcessor/Colors/Colorspaces/CieLab.cs

@@ -86,20 +86,16 @@ namespace ImageProcessor
             float y = (color.R * 0.2126F) + (color.G * 0.7152F) + (color.B * 0.0722F);
             float z = (color.R * 0.0193F) + (color.G * 0.1192F) + (color.B * 0.9505F);
 
-            x *= 100F;
-            y *= 100F;
-            z *= 100F;
-
             // Now to LAB
-            x /= 95.047F;
-            y /= 100F;
-            z /= 108.883F;
+            x /= 0.95047F;
+            //y /= 1F;
+            z /= 1.08883F;
 
-            x = x > 0.008856 ? (float) Math.Pow(x, 1F / 3F) : (7.787F * x) + (16F / 116F);
-            y = y > 0.008856 ? (float) Math.Pow(y, 1F / 3F) : (7.787F * y) + (16F / 116F);
-            z = z > 0.008856 ? (float) Math.Pow(z, 1F / 3F) : (7.787F * z) + (16F / 116F);
+            x = x > 0.008856F ? (float) Math.Pow(x, 1F / 3F) : (903.3F * x + 16F) / 116F;
+            y = y > 0.008856F ? (float) Math.Pow(y, 1F / 3F) : (903.3F * y + 16F) / 116F;
+            z = z > 0.008856F ? (float) Math.Pow(z, 1F / 3F) : (903.3F * z + 16F) / 116F;
 
-            float l = (116F * y) - 16F;
+            float l = Math.Max(0, (116F * y) - 16F);
             float a = 500F * (x - y);
             float b = 200F * (y - z);
 

tests/ImageProcessor.Tests/Colors/ColorConversionTests.cs

@@ -339,9 +339,6 @@ namespace ImageProcessor.Tests
         /// Tests the implicit conversion from <see cref="Color"/> to <see cref="CieLab"/>.
         /// Comparison values obtained from 
         /// http://colormine.org/convert/rgb-to-lab
-        /// http://au.mathworks.com/help/images/ref/rgb2lab.html
-        /// http://www.colorhexa.com/00ffff
-        /// L seems to match quite well, A and B tend to drift from the converter results a bit more
         /// </summary>
         [Fact]
         public void ColorToCieLab()
@@ -350,35 +347,37 @@ namespace ImageProcessor.Tests
             Color color = new Color(1, 1, 1);
             CieLab cielab = color;
 
-            Assert.Equal(100, cielab.L, 1);
-            Assert.Equal(0, cielab.A, 1);
-            Assert.Equal(0, cielab.B, 1);
+            Assert.Equal(100, cielab.L, 3);
+            Assert.Equal(0.005, cielab.A, 3);
+            Assert.Equal(-0.010, cielab.B, 3);
 
             // Black
             Color color2 = new Color(0, 0, 0);
             CieLab cielab2 = color2;
-            Assert.Equal(0, cielab2.L, 1);
-            Assert.Equal(0, cielab2.A, 1);
-            Assert.Equal(0, cielab2.B, 1);
+            Assert.Equal(0, cielab2.L, 3);
+            Assert.Equal(0, cielab2.A, 3);
+            Assert.Equal(0, cielab2.B, 3);
 
             //// Grey
             Color color3 = new Color(128 / 255f, 128 / 255f, 128 / 255f);
             CieLab cielab3 = color3;
-            Assert.Equal(53.6, cielab3.L, 1);
-            Assert.Equal(0, cielab3.A, 1);
-            Assert.Equal(0, cielab3.B, 1);
+            Assert.Equal(53.585, cielab3.L, 3);
+            Assert.Equal(0.003, cielab3.A, 3);
+            Assert.Equal(-0.006, cielab3.B, 3);
 
             //// Cyan
             Color color4 = new Color(0, 1, 1);
             CieLab cielab4 = color4;
-            Assert.Equal(91.1, cielab4.L, 1);
-            Assert.Equal(-48.1, cielab4.A, 1);
-            Assert.Equal(-14.1, cielab4.B, 1);
+            Assert.Equal(91.117, cielab4.L, 3);
+            Assert.Equal(-48.080, cielab4.A, 3);
+            Assert.Equal(-14.138, cielab4.B, 3);
         }
 
         /// <summary>
         /// Tests the implicit conversion from <see cref="CieLab"/> to <see cref="Color"/>.
         /// </summary>
+        /// Comparison values obtained from 
+        /// http://colormine.org/convert/rgb-to-lab
         [Fact]
         public void CieLabToColor()
         {
@@ -386,25 +385,25 @@ namespace ImageProcessor.Tests
             CieLab cielab = new CieLab(36.5492f, 33.3173f, -12.0615f);
             Color color = cielab;
 
-            Assert.Equal(color.R, 128 / 255f, 1);
-            Assert.Equal(color.G, 64 / 255f, 2);
-            Assert.Equal(color.B, 106 / 255f, 1);
+            Assert.Equal(color.R, 128 / 255f, 3);
+            Assert.Equal(color.G, 64 / 255f, 3);
+            Assert.Equal(color.B, 106 / 255f, 3);
 
             // Ochre
             CieLab cielab2 = new CieLab(58.1758f, 27.3399f, 56.8240f);
             Color color2 = cielab2;
 
-            Assert.Equal(color2.R, 204 / 255f, 1);
-            Assert.Equal(color2.G, 119 / 255f, 2);
-            Assert.Equal(color2.B, 34 / 255f, 1);
+            Assert.Equal(color2.R, 204 / 255f, 3);
+            Assert.Equal(color2.G, 119 / 255f, 3);
+            Assert.Equal(color2.B, 34 / 255f, 3);
 
             //// White
             CieLab cielab3 = new CieLab(0, 0, 0);
             Color color3 = cielab3;
 
-            Assert.Equal(color3.R, 0f, 1);
-            Assert.Equal(color3.G, 0f, 1);
-            Assert.Equal(color3.B, 0f, 1);
+            Assert.Equal(color3.R, 0f, 3);
+            Assert.Equal(color3.G, 0f, 3);
+            Assert.Equal(color3.B, 0f, 3);
 
             //// Check others.
             Random random = new Random(0);