Move PngHeader parsing logic to struct

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -943,17 +943,9 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// <param name="data">The <see cref="T:ReadOnlySpan{byte}"/> containing data.</param>
         private void ReadHeaderChunk(PngMetaData pngMetaData, ReadOnlySpan<byte> data)
         {
-            byte bitDepth = data[8];
-            this.header = new PngHeader(
-                width: BinaryPrimitives.ReadInt32BigEndian(data.Slice(0, 4)),
-                height: BinaryPrimitives.ReadInt32BigEndian(data.Slice(4, 4)),
-                bitDepth: bitDepth,
-                colorType: (PngColorType)data[9],
-                compressionMethod: data[10],
-                filterMethod: data[11],
-                interlaceMethod: (PngInterlaceMode)data[12]);
-
-            pngMetaData.BitDepth = (PngBitDepth)bitDepth;
+            this.header = PngHeader.Parse(data);
+
+            pngMetaData.BitDepth = (PngBitDepth)this.header.BitDepth;
             pngMetaData.ColorType = this.header.ColorType;
         }
 

src/ImageSharp/Formats/Png/PngHeader.cs

@@ -1,6 +1,9 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
+using System.Buffers.Binary;
+
 namespace SixLabors.ImageSharp.Formats.Png
 {
     /// <summary>
@@ -74,5 +77,22 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// Two values are currently defined: 0 (no interlace) or 1 (Adam7 interlace).
         /// </summary>
         public PngInterlaceMode InterlaceMethod { get; }
+
+        /// <summary>
+        /// Parses the PngHeader from the given data buffer.
+        /// </summary>
+        /// <param name="data">The data to parse.</param>
+        /// <returns>The parsed PngHeader.</returns>
+        public static PngHeader Parse(ReadOnlySpan<byte> data)
+        {
+            return new PngHeader(
+              width: BinaryPrimitives.ReadInt32BigEndian(data.Slice(0, 4)),
+              height: BinaryPrimitives.ReadInt32BigEndian(data.Slice(4, 4)),
+              bitDepth: data[8],
+              colorType: (PngColorType)data[9],
+              compressionMethod: data[10],
+              filterMethod: data[11],
+              interlaceMethod: (PngInterlaceMode)data[12]);
+        }
     }
 }