format detector for BigTiff

src/ImageSharp/Formats/Tiff/TiffConfigurationModule.cs

@@ -13,7 +13,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         {
             configuration.ImageFormatsManager.SetEncoder(TiffFormat.Instance, new TiffEncoder());
             configuration.ImageFormatsManager.SetDecoder(TiffFormat.Instance, new TiffDecoder());
-            configuration.ImageFormatsManager.AddImageFormatDetector(new TiffImageFormatDetector());
+            configuration.ImageFormatsManager.AddImageFormatDetector(new TiffImageFormatDetector(false));
         }
     }
-}
+}

src/ImageSharp/Formats/Tiff/TiffImageFormatDetector.cs

@@ -10,8 +10,16 @@ namespace SixLabors.ImageSharp.Formats.Tiff
     /// </summary>
     public sealed class TiffImageFormatDetector : IImageFormatDetector
     {
+        private readonly bool isBigTiff;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="TiffImageFormatDetector"/> class.
+        /// </summary>
+        /// <param name="isBigTiff">if set to <c>true</c> [is big tiff].</param>
+        public TiffImageFormatDetector(bool isBigTiff) => this.isBigTiff = isBigTiff;
+
         /// <inheritdoc/>
-        public int HeaderSize => 4;
+        public int HeaderSize => this.isBigTiff ? 8 : 4;
 
         /// <inheritdoc/>
         public IImageFormat DetectFormat(ReadOnlySpan<byte> header)
@@ -26,9 +34,52 @@ namespace SixLabors.ImageSharp.Formats.Tiff
 
         private bool IsSupportedFileFormat(ReadOnlySpan<byte> header)
         {
-            return header.Length >= this.HeaderSize &&
-                   ((header[0] == 0x49 && header[1] == 0x49 && header[2] == 0x2A && header[3] == 0x00) || // Little-endian
-                    (header[0] == 0x4D && header[1] == 0x4D && header[2] == 0x00 && header[3] == 0x2A)); // Big-endian
+            if (header.Length >= this.HeaderSize)
+            {
+                if (header[0] == 0x49 && header[1] == 0x49)
+                {
+                    // Little-endian
+                    if (!this.isBigTiff)
+                    {
+                        if (header[2] == 0x2A && header[3] == 0x00)
+                        {
+                            return true;
+                        }
+                    }
+                    else
+                    {
+                        if (header[2] == 0x2B && header[3] == 0x00 && header[4] == 8 && header[5] == 0 && header[6] == 0 && header[7] == 0)
+                        {
+                            return true;
+                        }
+                    }
+                }
+                else if (header[0] == 0x4D && header[1] == 0x4D)
+                {
+                    // Big-endian
+                    if (header[2] == 0x00 && (header[3] == 0x2A || header[3] == 0x2B))
+                    {
+                        return true;
+                    }
+
+                    if (!this.isBigTiff)
+                    {
+                        if (header[2] == 0 && header[3] == 0x2A)
+                        {
+                            return true;
+                        }
+                    }
+                    else
+                    {
+                        if (header[2] == 0 && header[3] == 0x2A && header[4] == 0 && header[5] == 8 && header[6] == 0 && header[7] == 0)
+                        {
+                            return true;
+                        }
+                    }
+                }
+            }
+
+            return false;
         }
     }
-}
+}