Added AssumeAlpha to the TiffReadDefines.

Author: dlemstra

src/Magick.NET/Formats/Tiff/TiffReadDefines.cs

@@ -11,6 +11,11 @@ namespace ImageMagick.Formats;
 /// </summary>
 public sealed class TiffReadDefines : IReadDefines
 {
+    /// <summary>
+    /// Gets or sets a value indicating whether to assume that a single extra sample is an alpha channel (tiff:assume-alpha).
+    /// </summary>
+    public bool? AssumeAlpha { get; set; }
+
     /// <summary>
     /// Gets the format where the defines are for.
     /// </summary>
@@ -49,6 +54,9 @@ public IEnumerable<IDefine> Defines
     {
         get
         {
+            if (AssumeAlpha is not null)
+                yield return new MagickDefine(Format, "assume-alpha", AssumeAlpha.Value);
+
             if (IgnoreExifProperties.Equals(true))
                 yield return new MagickDefine(Format, "exif-properties", false);
 

tests/Magick.NET.Tests/Formats/Tiff/TiffReadDefinesTests/TheAssumeAlphaProperty.cs

@@ -0,0 +1,26 @@
+// Copyright Dirk Lemstra https://github.com/dlemstra/Magick.NET.
+// Licensed under the Apache License, Version 2.0.
+
+using ImageMagick;
+using ImageMagick.Formats;
+using Xunit;
+
+namespace Magick.NET.Tests;
+
+public partial class TiffReadDefinesTests
+{
+    public class TheAssumeAlphaProperty
+    {
+        [Fact]
+        public void ShouldSetTheDefine()
+        {
+            using var image = new MagickImage();
+            image.Settings.SetDefines(new TiffReadDefines
+            {
+                AssumeAlpha = true,
+            });
+
+            Assert.Equal("true", image.Settings.GetDefine(MagickFormat.Tiff, "assume-alpha"));
+        }
+    }
+}

tests/Magick.NET.Tests/Formats/Tiff/TiffReadDefinesTests/TheConstructor.cs

@@ -17,6 +17,7 @@ public void ShouldNotSetAnyDefine()
             using var image = new MagickImage();
             image.Settings.SetDefines(new TiffReadDefines());
 
+            Assert.Null(image.Settings.GetDefine(MagickFormat.Tiff, "assume-alpha"));
             Assert.Null(image.Settings.GetDefine(MagickFormat.Tiff, "exif-properties"));
             Assert.Null(image.Settings.GetDefine(MagickFormat.Tiff, "ignore-layers"));
             Assert.Null(image.Settings.GetDefine(MagickFormat.Tiff, "ignore-tags"));