Added CICP metadata handling to PNG de/encoder

Author: VentuzTammoHinrichs

src/ImageSharp/Formats/Png/PngChunkType.cs

@@ -140,6 +140,12 @@ internal enum PngChunkType : uint
     /// <remarks>cHRM (Single)</remarks>
     Chroma = 0x6348524d,
 
+    /// <summary>
+    /// If this chunk is present, it specifies the color space, transfer function, matrix coefficients of the image
+    /// using the code points specified in [ITU-T-H.273]
+    /// </summary>
+    Cicp = 0x63494350,
+
     /// <summary>
     /// This chunk is an ancillary chunk as defined in the PNG Specification.
     /// It must appear before the first IDAT chunk within a valid PNG stream.

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -16,6 +16,7 @@
 using SixLabors.ImageSharp.IO;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
+using SixLabors.ImageSharp.Metadata.Profiles.CICP;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.Metadata.Profiles.Icc;
 using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
@@ -183,6 +184,9 @@ public Image<TPixel> Decode<TPixel>(BufferedReadStream stream, CancellationToken
                         case PngChunkType.Gamma:
                             ReadGammaChunk(pngMetadata, chunk.Data.GetSpan());
                             break;
+                        case PngChunkType.Cicp:
+                            ReadCicpChunk(metadata, chunk.Data.GetSpan());
+                            break;
                         case PngChunkType.FrameControl:
                             frameCount++;
                             if (frameCount == this.maxFrames)
@@ -352,6 +356,15 @@ public ImageInfo Identify(BufferedReadStream stream, CancellationToken cancellat
 
                             ReadGammaChunk(pngMetadata, chunk.Data.GetSpan());
                             break;
+                        case PngChunkType.Cicp:
+                            if (this.colorMetadataOnly)
+                            {
+                                this.SkipChunkDataAndCrc(chunk);
+                                break;
+                            }
+
+                            ReadCicpChunk(metadata, chunk.Data.GetSpan());
+                            break;
                         case PngChunkType.FrameControl:
                             ++frameCount;
                             if (frameCount == this.maxFrames)
@@ -1392,6 +1405,26 @@ private static bool TryReadTextChunkMetadata(ImageMetadata baseMetadata, string
         return false;
     }
 
+    /// <summary>
+    /// Reads the CICP color profile chunk.
+    /// </summary>
+    /// <param name="metadata">The metadata.</param>
+    /// <param name="data">The bytes containing the profile.</param>
+    private static void ReadCicpChunk(ImageMetadata metadata, ReadOnlySpan<byte> data)
+    {
+        if (data.Length < 4)
+        {
+            // Ignore invalid cICP chunks.
+            return;
+        }
+
+        byte colorPrimaries = data[0];
+        byte transferFunction = data[1];
+        byte matrixCoefficients = data[2];
+        bool? fullRange = data[3] == 1 ? true : data[3] == 0 ? false : null;
+        metadata.CicpProfile = new CicpProfile(colorPrimaries, transferFunction, matrixCoefficients, fullRange);
+    }
+
     /// <summary>
     /// Reads exif data encoded into a text chunk with the name "raw profile type exif".
     /// This method was used by ImageMagick, exiftool, exiv2, digiKam, etc, before the

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -166,6 +166,7 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
 
         this.WriteHeaderChunk(stream);
         this.WriteGammaChunk(stream);
+        this.WriteCicpChunk(stream, metadata);
         this.WriteColorProfileChunk(stream, metadata);
         this.WritePaletteChunk(stream, quantized);
         this.WriteTransparencyChunk(stream, pngMetadata);
@@ -773,6 +774,26 @@ private void WriteXmpChunk(Stream stream, ImageMetadata meta)
         this.WriteChunk(stream, PngChunkType.InternationalText, payload);
     }
 
+    /// <summary>
+    /// Writes the CICP profile chunk
+    /// </summary>
+    /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
+    /// <param name="metaData">The image meta data.</param>
+    private void WriteCicpChunk(Stream stream, ImageMetadata metaData)
+    {
+        if (metaData.CicpProfile is null)
+        {
+            return;
+        }
+
+        Span<byte> outputBytes = this.chunkDataBuffer.Span[..4];
+        outputBytes[0] = (byte)metaData.CicpProfile.ColorPrimaries;
+        outputBytes[1] = (byte)metaData.CicpProfile.TransferCharacteristics;
+        outputBytes[2] = (byte)metaData.CicpProfile.MatrixCoefficients;
+        outputBytes[3] = (byte)(metaData.CicpProfile.FullRange ? 1 : 0);
+        this.WriteChunk(stream, PngChunkType.Cicp, outputBytes);
+    }
+
     /// <summary>
     /// Writes the color profile chunk.
     /// </summary>

tests/ImageSharp.Tests/Formats/Png/PngChunkTypeTests.cs

@@ -29,6 +29,7 @@ public void ChunkTypeIdsAreCorrect()
         Assert.Equal(PngChunkType.Background, GetType("bKGD"));
         Assert.Equal(PngChunkType.EmbeddedColorProfile, GetType("iCCP"));
         Assert.Equal(PngChunkType.StandardRgbColourSpace, GetType("sRGB"));
+        Assert.Equal(PngChunkType.Cicp, GetType("cICP"));
         Assert.Equal(PngChunkType.SignificantBits, GetType("sBIT"));
         Assert.Equal(PngChunkType.Histogram, GetType("hIST"));
         Assert.Equal(PngChunkType.SuggestedPalette, GetType("sPLT"));