added EXIF chunk type and setting ExifProfile, if eXIf chunk data is present (#611)

src/ImageSharp/Formats/Png/PngChunkType.cs

@@ -4,7 +4,7 @@
 namespace SixLabors.ImageSharp.Formats.Png
 {
     /// <summary>
-    /// Contains a list of of chunk types.
+    /// Contains a list of chunk types.
     /// </summary>
     internal enum PngChunkType : uint
     {
@@ -55,6 +55,11 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// <summary>
         /// The pHYs chunk specifies the intended pixel size or aspect ratio for display of the image.
         /// </summary>
-        Physical = 0x70485973U // pHYs
+        Physical = 0x70485973U, // pHYs
+
+        /// <summary>
+        /// The data chunk which contains the Exif profile.
+        /// </summary>
+        Exif = 0x65584966U // eXIf
     }
 }

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -15,6 +15,7 @@ using SixLabors.ImageSharp.Formats.Png.Filters;
 using SixLabors.ImageSharp.Formats.Png.Zlib;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.MetaData;
+using SixLabors.ImageSharp.MetaData.Profiles.Exif;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Png
@@ -250,6 +251,11 @@ namespace SixLabors.ImageSharp.Formats.Png
                                 case PngChunkType.Text:
                                     this.ReadTextChunk(metadata, chunk.Data.Array, chunk.Length);
                                     break;
+                                case PngChunkType.Exif:
+                                    byte[] exifData = new byte[chunk.Length];
+                                    Buffer.BlockCopy(chunk.Data.Array, 0, exifData, 0, chunk.Length);
+                                    metadata.ExifProfile = new ExifProfile(exifData);
+                                    break;
                                 case PngChunkType.End:
                                     this.isEndChunkReached = true;
                                     break;