Added a couple of tests for CicpProfile

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -786,6 +786,12 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
             return;
         }
 
+        // by spec, the matrix coefficients must be set to Identity
+        if (metaData.CicpProfile.MatrixCoefficients != Metadata.Profiles.CICP.CicpMatrixCoefficients.Identity)
+        {
+            throw new NotSupportedException("CICP matrix coefficients other than Identity are not supported in PNG");
+        }
+
         Span<byte> outputBytes = this.chunkDataBuffer.Span[..4];
         outputBytes[0] = (byte)metaData.CicpProfile.ColorPrimaries;
         outputBytes[1] = (byte)metaData.CicpProfile.TransferCharacteristics;

tests/ImageSharp.Tests/Metadata/Profiles/CICP/CicpProfileTests.cs

@@ -0,0 +1,72 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats;
+using SixLabors.ImageSharp.Formats.Png;
+using SixLabors.ImageSharp.Metadata.Profiles.CICP;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Tests.Metadata.Profiles.Cicp;
+
+public class CicpProfileTests
+{
+    [Theory]
+    [WithFile(TestImages.Png.AdamHeadsHlg, PixelTypes.Rgba64)]
+    public async Task ReadCicpMetadata_FromPng_Works<TPixel>(TestImageProvider<TPixel> provider)
+       where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using (Image<TPixel> image = await provider.GetImageAsync(PngDecoder.Instance))
+        {
+            CicpProfile actual = image.Metadata.CicpProfile ?? image.Frames.RootFrame.Metadata.CicpProfile;
+            CicpProfileContainsExpectedValues(actual);
+        }
+    }
+
+    [Fact]
+    public void WritingPng_PreservesCicpProfile()
+    {
+        // arrange
+        using var image = new Image<Rgba32>(1, 1);
+        var original = new CicpProfile()
+        {
+            ColorPrimaries = CicpColorPrimaries.ItuRBt2020_2,
+            TransferCharacteristics = CicpTransferCharacteristics.SmpteSt2084,
+            MatrixCoefficients = CicpMatrixCoefficients.Identity,
+            FullRange = true,
+        };
+        image.Metadata.CicpProfile = original;
+        var encoder = new PngEncoder();
+
+        // act
+        using Image<Rgba32> reloadedImage = WriteAndRead(image, encoder);
+
+        // assert
+        CicpProfile actual = reloadedImage.Metadata.CicpProfile ?? reloadedImage.Frames.RootFrame.Metadata.CicpProfile;
+        Assert.NotNull(actual);
+        Assert.Equal(actual.ColorPrimaries, original.ColorPrimaries);
+        Assert.Equal(actual.TransferCharacteristics, original.TransferCharacteristics);
+        Assert.Equal(actual.MatrixCoefficients, original.MatrixCoefficients);
+        Assert.Equal(actual.FullRange, original.FullRange);
+    }
+
+    private static void CicpProfileContainsExpectedValues(CicpProfile cicp)
+    {
+        Assert.NotNull(cicp);
+        Assert.Equal(CicpColorPrimaries.ItuRBt2020_2, cicp.ColorPrimaries);
+        Assert.Equal(CicpTransferCharacteristics.AribStdB67, cicp.TransferCharacteristics);
+        Assert.Equal(CicpMatrixCoefficients.Identity, cicp.MatrixCoefficients);
+        Assert.True(cicp.FullRange);
+    }
+
+    private static Image<Rgba32> WriteAndRead(Image<Rgba32> image, IImageEncoder encoder)
+    {
+        using (var memStream = new MemoryStream())
+        {
+            image.Save(memStream, encoder);
+            image.Dispose();
+
+            memStream.Position = 0;
+            return Image.Load<Rgba32>(memStream);
+        }
+    }
+}

tests/ImageSharp.Tests/TestImages.cs

@@ -61,6 +61,7 @@ public static class TestImages
         public const string TestPattern31x31 = "Png/testpattern31x31.png";
         public const string TestPattern31x31HalfTransparent = "Png/testpattern31x31-halftransparent.png";
         public const string XmpColorPalette = "Png/xmp-colorpalette.png";
+        public const string AdamHeadsHlg = "Png/adamHeadsHLG.png";
 
         // Animated
         // https://philip.html5.org/tests/apng/tests.html

tests/Images/Input/Png/adamheadsHLG.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:8c50691da3b3af21ff4f8fc30f1313bc412b84fb0a07a5bf3b8b14eae7581ade
+size 201440