Added OffIfOpaque to AlphaOption.

Author: dlemstra

src/Magick.NET.Core/Enums/AlphaOption.cs

@@ -101,4 +101,9 @@ public enum AlphaOption
     /// RGB data still intact, but fully transparent.
     /// </summary>
     Transparent,
+
+    /// <summary>
+    /// Removes the alpha channel when the alpha value is opaque for all pixels.
+    /// </summary>
+    OffIfOpaque,
 }

tests/Magick.NET.Tests/MagickImageTests/TheAlphaMethod.cs

@@ -36,5 +36,35 @@ public void ShouldUseTheBackgroundColor()
             Assert.False(image.HasAlpha);
             ColorAssert.Equal(new MagickColor(Quantum.Max, 0, 0), image, 0, 0);
         }
+
+        [Fact]
+        public void ShouldRemoveAlphaChannelIfAllPixelsAreOpaque()
+        {
+            using var image = new MagickImage(MagickColors.Red, 2, 2);
+            image.Alpha(AlphaOption.On);
+
+            Assert.True(image.HasAlpha);
+
+            image.Alpha(AlphaOption.OffIfOpaque);
+
+            Assert.False(image.HasAlpha);
+        }
+
+        [Fact]
+        public void ShouldKeepAlphaChannelIfSinglePixesIsNotOpaque()
+        {
+            using var image = new MagickImage(MagickColors.Red, 2, 2);
+            image.Alpha(AlphaOption.On);
+
+            Assert.True(image.HasAlpha);
+
+            using var pixels = image.GetPixels();
+            var pixel = pixels.GetPixel(1, 1);
+            pixel[3] = 0;
+
+            image.Alpha(AlphaOption.OffIfOpaque);
+
+            Assert.True(image.HasAlpha);
+        }
     }
 }