Declare UTF-8 in IPTC data written from cloned profiles

src/ImageSharp/Metadata/Profiles/IPTC/IptcProfile.cs

@@ -228,6 +228,10 @@ public void SetDateTimeValue(IptcTag tag, DateTimeOffset dateTimeOffset)
     /// <summary>
     /// Updates the data of the profile.
     /// </summary>
+    /// <remarks>
+    /// When any value uses UTF-8 encoding, which is the default encoding of a value, the data starts with the
+    /// 1:90 Coded Character Set dataset declaring UTF-8, also when the text is ASCII only.
+    /// </remarks>
     public void UpdateData()
     {
         int length = 0;
@@ -337,7 +341,9 @@ private bool HasValuesInUtf8()
     {
         foreach (IptcValue value in this.values)
         {
-            if (value.Encoding == Encoding.UTF8)
+            // Compare the code page rather than the instance. Cloned values hold a copy of their encoding,
+            // and callers can pass their own UTF8Encoding, but both still write UTF-8 bytes.
+            if (value.Encoding.CodePage == Encoding.UTF8.CodePage)
             {
                 return true;
             }

tests/ImageSharp.Tests/Metadata/Profiles/IPTC/IptcProfileTests.cs

@@ -34,6 +34,57 @@ public void IptcProfile_WithUtf8Data_WritesEnvelopeRecord_Works()
         Assert.True(profileBytes.AsSpan(0, 8).SequenceEqual(expectedEnvelopeData));
     }
 
+    [Fact]
+    public void IptcProfile_DeepClone_WithUtf8Data_WritesEnvelopeRecord_Works()
+    {
+        // arrange
+        IptcProfile profile = new();
+        profile.SetValue(IptcTag.City, "ESPAÑA");
+        IptcProfile clone = profile.DeepClone();
+        byte[] expectedEnvelopeData = [28, 1, 90, 0, 3, 27, 37, 71];
+
+        // act
+        clone.UpdateData();
+
+        // assert
+        Assert.True(clone.Data.AsSpan(0, 8).SequenceEqual(expectedEnvelopeData));
+    }
+
+    [Fact]
+    public void IptcProfile_WithUtf8EncodingInstance_WritesEnvelopeRecord_Works()
+    {
+        // arrange
+        IptcProfile profile = new();
+        profile.SetValue(IptcTag.City, new System.Text.UTF8Encoding(false), "ESPAÑA");
+        byte[] expectedEnvelopeData = [28, 1, 90, 0, 3, 27, 37, 71];
+
+        // act
+        profile.UpdateData();
+
+        // assert
+        Assert.True(profile.Data.AsSpan(0, 8).SequenceEqual(expectedEnvelopeData));
+    }
+
+    [Fact]
+    public void WritingClonedImage_WithUtf8Data_WritesEnvelopeRecordOnce()
+    {
+        // arrange
+        using Image<Rgba32> image = new(1, 1);
+        image.Metadata.IptcProfile = new IptcProfile();
+        image.Metadata.IptcProfile.SetValue(IptcTag.Caption, "ESPAÑA");
+        byte[] expectedData = [28, 1, 90, 0, 3, 27, 37, 71, 28, 2, 120, 0, 7, 69, 83, 80, 65, 195, 145, 65];
+
+        // act
+        using Image<Rgba32> once = WriteAndReadJpeg(image.Clone());
+        using Image<Rgba32> twice = WriteAndReadJpeg(once.Clone());
+
+        // assert
+        IptcProfile actual = twice.Metadata.IptcProfile;
+        Assert.Equal(expectedData, actual.Data);
+        IptcValue value = Assert.Single(actual.Values);
+        Assert.Equal("ESPAÑA", value.Value);
+    }
+
     [Theory]
     [MemberData(nameof(AllIptcTags))]
     public void IptcProfile_SetValue_WithStrictEnabled_Works(IptcTag tag)