Moved HeaderSize and IsSupportedFileFormat to IImageFormat.

src/ImageSharp/Formats/Bmp/BmpDecoder.cs

@@ -25,32 +25,6 @@ namespace ImageSharp.Formats
     /// </remarks>
     public class BmpDecoder : IImageDecoder
     {
-        /// <summary>
-        /// Gets the size of the header for this image type.
-        /// </summary>
-        /// <value>The size of the header.</value>
-        public int HeaderSize => 2;
-
-        /// <summary>
-        /// Returns a value indicating whether the <see cref="IImageDecoder"/> supports the specified
-        /// file header.
-        /// </summary>
-        /// <param name="header">The <see cref="T:byte[]"/> containing the file header.</param>
-        /// <returns>
-        /// True if the decoder supports the file header; otherwise, false.
-        /// </returns>
-        public bool IsSupportedFileFormat(byte[] header)
-        {
-            bool isBmp = false;
-            if (header.Length >= 2)
-            {
-                isBmp = header[0] == 0x42 && // B
-                        header[1] == 0x4D;   // M
-            }
-
-            return isBmp;
-        }
-
         /// <inheritdoc/>
         public void Decode<TColor, TPacked>(Image<TColor, TPacked> image, Stream stream)
         where TColor : struct, IPackedPixel<TPacked>

src/ImageSharp/Formats/Bmp/BmpFormat.cs

@@ -26,5 +26,21 @@ namespace ImageSharp.Formats
 
         /// <inheritdoc/>
         public IImageEncoder Encoder => new BmpEncoder();
+
+        /// <inheritdoc/>
+        public int HeaderSize => 2;
+
+        /// <inheritdoc/>
+        public bool IsSupportedFileFormat(byte[] header)
+        {
+            bool isBmp = false;
+            if (header.Length >= this.HeaderSize)
+            {
+                isBmp = header[0] == 0x42 && // B
+                        header[1] == 0x4D;   // M
+            }
+
+            return isBmp;
+        }
     }
 }

src/ImageSharp/Formats/Gif/GifDecoder.cs

@@ -13,31 +13,6 @@ namespace ImageSharp.Formats
     /// </summary>
     public class GifDecoder : IImageDecoder
     {
-        /// <summary>
-        /// Gets the size of the header for this image type.
-        /// </summary>
-        /// <value>The size of the header.</value>
-        public int HeaderSize => 6;
-
-        /// <summary>
-        /// Returns a value indicating whether the <see cref="IImageDecoder"/> supports the specified
-        /// file header.
-        /// </summary>
-        /// <param name="header">The <see cref="T:byte[]"/> containing the file header.</param>
-        /// <returns>
-        /// True if the decoder supports the file header; otherwise, false.
-        /// </returns>
-        public bool IsSupportedFileFormat(byte[] header)
-        {
-            return header.Length >= 6 &&
-                   header[0] == 0x47 && // G
-                   header[1] == 0x49 && // I
-                   header[2] == 0x46 && // F
-                   header[3] == 0x38 && // 8
-                  (header[4] == 0x39 || header[4] == 0x37) && // 9 or 7
-                   header[5] == 0x61;   // a
-        }
-
         /// <inheritdoc/>
         public void Decode<TColor, TPacked>(Image<TColor, TPacked> image, Stream stream)
             where TColor : struct, IPackedPixel<TPacked>

src/ImageSharp/Formats/Gif/GifFormat.cs

@@ -26,5 +26,20 @@ namespace ImageSharp.Formats
 
         /// <inheritdoc/>
         public IImageEncoder Encoder => new GifEncoder();
+
+        /// <inheritdoc/>
+        public int HeaderSize => 6;
+
+        /// <inheritdoc/>
+        public bool IsSupportedFileFormat(byte[] header)
+        {
+            return header.Length >= this.HeaderSize &&
+                   header[0] == 0x47 && // G
+                   header[1] == 0x49 && // I
+                   header[2] == 0x46 && // F
+                   header[3] == 0x38 && // 8
+                  (header[4] == 0x39 || header[4] == 0x37) && // 9 or 7
+                   header[5] == 0x61;   // a
+        }
     }
 }

src/ImageSharp/Formats/IImageDecoder.cs

@@ -13,22 +13,6 @@ namespace ImageSharp.Formats
     /// </summary>
     public interface IImageDecoder
     {
-        /// <summary>
-        /// Gets the size of the header for this image type.
-        /// </summary>
-        /// <value>The size of the header.</value>
-        int HeaderSize { get; }
-
-        /// <summary>
-        /// Returns a value indicating whether the <see cref="IImageDecoder"/> supports the specified
-        /// file header.
-        /// </summary>
-        /// <param name="header">The <see cref="T:byte[]"/> containing the file header.</param>
-        /// <returns>
-        /// True if the decoder supports the file header; otherwise, false.
-        /// </returns>
-        bool IsSupportedFileFormat(byte[] header);
-
         /// <summary>
         /// Decodes the image from the specified stream to the <see cref="ImageBase{TColor, TPacked}"/>.
         /// </summary>

src/ImageSharp/Formats/IImageFormat.cs

@@ -39,5 +39,21 @@ namespace ImageSharp.Formats
         /// Gets the image decoder for decoding an image from a stream.
         /// </summary>
         IImageDecoder Decoder { get; }
+
+        /// <summary>
+        /// Gets the size of the header for this image type.
+        /// </summary>
+        /// <value>The size of the header.</value>
+        int HeaderSize { get; }
+
+        /// <summary>
+        /// Returns a value indicating whether the <see cref="IImageDecoder"/> supports the specified
+        /// file header.
+        /// </summary>
+        /// <param name="header">The <see cref="T:byte[]"/> containing the file header.</param>
+        /// <returns>
+        /// True if the decoder supports the file header; otherwise, false.
+        /// </returns>
+        bool IsSupportedFileFormat(byte[] header);
     }
 }

src/ImageSharp/Formats/Jpg/JpegDecoder.cs

@@ -13,41 +13,6 @@ namespace ImageSharp.Formats
     /// </summary>
     public class JpegDecoder : IImageDecoder
     {
-        /// <summary>
-        /// Gets the size of the header for this image type.
-        /// </summary>
-        /// <value>The size of the header.</value>
-        public int HeaderSize => 11;
-
-        /// <summary>
-        /// Indicates if the image decoder supports the specified
-        /// file header.
-        /// </summary>
-        /// <param name="header">The file header.</param>
-        /// <returns>
-        /// <c>true</c>, if the decoder supports the specified
-        /// file header; otherwise <c>false</c>.
-        /// </returns>
-        /// <exception cref="System.ArgumentNullException"><paramref name="header"/>
-        /// is null (Nothing in Visual Basic).</exception>
-        public bool IsSupportedFileFormat(byte[] header)
-        {
-            Guard.NotNull(header, "header");
-
-            bool isSupported = false;
-
-            if (header.Length >= 11)
-            {
-                bool isJfif = IsJfif(header);
-                bool isExif = IsExif(header);
-                bool isJpeg = IsJpeg(header);
-
-                isSupported = isJfif || isExif || isJpeg;
-            }
-
-            return isSupported;
-        }
-
         /// <inheritdoc/>
         public void Decode<TColor, TPacked>(Image<TColor, TPacked> image, Stream stream)
             where TColor : struct, IPackedPixel<TPacked>
@@ -61,54 +26,5 @@ namespace ImageSharp.Formats
                 decoder.Decode(image, stream, false);
             }
         }
-
-        /// <summary>
-        /// Returns a value indicating whether the given bytes identify Jfif data.
-        /// </summary>
-        /// <param name="header">The bytes representing the file header.</param>
-        /// <returns>The <see cref="bool"/></returns>
-        private static bool IsJfif(byte[] header)
-        {
-            bool isJfif =
-                header[6] == 0x4A && // J
-                header[7] == 0x46 && // F
-                header[8] == 0x49 && // I
-                header[9] == 0x46 && // F
-                header[10] == 0x00;
-
-            return isJfif;
-        }
-
-        /// <summary>
-        /// Returns a value indicating whether the given bytes identify EXIF data.
-        /// </summary>
-        /// <param name="header">The bytes representing the file header.</param>
-        /// <returns>The <see cref="bool"/></returns>
-        private static bool IsExif(byte[] header)
-        {
-            bool isExif =
-                header[6] == 0x45 && // E
-                header[7] == 0x78 && // X
-                header[8] == 0x69 && // I
-                header[9] == 0x66 && // F
-                header[10] == 0x00;
-
-            return isExif;
-        }
-
-        /// <summary>
-        /// Returns a value indicating whether the given bytes identify Jpeg data.
-        /// This is a last chance resort for jpegs that contain ICC information.
-        /// </summary>
-        /// <param name="header">The bytes representing the file header.</param>
-        /// <returns>The <see cref="bool"/></returns>
-        private static bool IsJpeg(byte[] header)
-        {
-            bool isJpg =
-                header[0] == 0xFF && // 255
-                header[1] == 0xD8; // 216
-
-            return isJpg;
-        }
     }
 }

src/ImageSharp/Formats/Jpg/JpegFormat.cs

@@ -26,5 +26,76 @@ namespace ImageSharp.Formats
 
         /// <inheritdoc/>
         public IImageEncoder Encoder => new JpegEncoder();
+
+        /// <inheritdoc/>
+        public int HeaderSize => 11;
+
+        /// <inheritdoc/>
+        public bool IsSupportedFileFormat(byte[] header)
+        {
+            Guard.NotNull(header, "header");
+
+            bool isSupported = false;
+
+            if (header.Length >= this.HeaderSize)
+            {
+                bool isJfif = IsJfif(header);
+                bool isExif = IsExif(header);
+                bool isJpeg = IsJpeg(header);
+
+                isSupported = isJfif || isExif || isJpeg;
+            }
+
+            return isSupported;
+        }
+
+        /// <summary>
+        /// Returns a value indicating whether the given bytes identify Jfif data.
+        /// </summary>
+        /// <param name="header">The bytes representing the file header.</param>
+        /// <returns>The <see cref="bool"/></returns>
+        private static bool IsJfif(byte[] header)
+        {
+            bool isJfif =
+                header[6] == 0x4A && // J
+                header[7] == 0x46 && // F
+                header[8] == 0x49 && // I
+                header[9] == 0x46 && // F
+                header[10] == 0x00;
+
+            return isJfif;
+        }
+
+        /// <summary>
+        /// Returns a value indicating whether the given bytes identify EXIF data.
+        /// </summary>
+        /// <param name="header">The bytes representing the file header.</param>
+        /// <returns>The <see cref="bool"/></returns>
+        private static bool IsExif(byte[] header)
+        {
+            bool isExif =
+                header[6] == 0x45 && // E
+                header[7] == 0x78 && // X
+                header[8] == 0x69 && // I
+                header[9] == 0x66 && // F
+                header[10] == 0x00;
+
+            return isExif;
+        }
+
+        /// <summary>
+        /// Returns a value indicating whether the given bytes identify Jpeg data.
+        /// This is a last chance resort for jpegs that contain ICC information.
+        /// </summary>
+        /// <param name="header">The bytes representing the file header.</param>
+        /// <returns>The <see cref="bool"/></returns>
+        private static bool IsJpeg(byte[] header)
+        {
+            bool isJpg =
+                header[0] == 0xFF && // 255
+                header[1] == 0xD8; // 216
+
+            return isJpg;
+        }
     }
 }

src/ImageSharp/Formats/Png/PngDecoder.cs

@@ -30,33 +30,6 @@ namespace ImageSharp.Formats
     /// </remarks>
     public class PngDecoder : IImageDecoder
     {
-        /// <summary>
-        /// Gets the size of the header for this image type.
-        /// </summary>
-        /// <value>The size of the header.</value>
-        public int HeaderSize => 8;
-
-        /// <summary>
-        /// Returns a value indicating whether the <see cref="IImageDecoder"/> supports the specified
-        /// file header.
-        /// </summary>
-        /// <param name="header">The <see cref="T:byte[]"/> containing the file header.</param>
-        /// <returns>
-        /// True if the decoder supports the file header; otherwise, false.
-        /// </returns>
-        public bool IsSupportedFileFormat(byte[] header)
-        {
-            return header.Length >= 8 &&
-                   header[0] == 0x89 &&
-                   header[1] == 0x50 && // P
-                   header[2] == 0x4E && // N
-                   header[3] == 0x47 && // G
-                   header[4] == 0x0D && // CR
-                   header[5] == 0x0A && // LF
-                   header[6] == 0x1A && // EOF
-                   header[7] == 0x0A;   // LF
-        }
-
         /// <summary>
         /// Decodes the image from the specified stream to the <see cref="ImageBase{TColor, TPacked}"/>.
         /// </summary>

src/ImageSharp/Formats/Png/PngFormat.cs

@@ -26,5 +26,22 @@ namespace ImageSharp.Formats
 
         /// <inheritdoc/>
         public IImageEncoder Encoder => new PngEncoder();
+
+        /// <inheritdoc/>
+        public int HeaderSize => 8;
+
+        /// <inheritdoc/>
+        public bool IsSupportedFileFormat(byte[] header)
+        {
+            return header.Length >= this.HeaderSize &&
+                   header[0] == 0x89 &&
+                   header[1] == 0x50 && // P
+                   header[2] == 0x4E && // N
+                   header[3] == 0x47 && // G
+                   header[4] == 0x0D && // CR
+                   header[5] == 0x0A && // LF
+                   header[6] == 0x1A && // EOF
+                   header[7] == 0x0A;   // LF
+        }
     }
 }

src/ImageSharp/Image/Image.cs

@@ -399,7 +399,7 @@ namespace ImageSharp
         /// </returns>
         private bool Decode(Stream stream)
         {
-            int maxHeaderSize = Bootstrapper.ImageFormats.Max(x => x.Decoder.HeaderSize);
+            int maxHeaderSize = Bootstrapper.ImageFormats.Max(x => x.HeaderSize);
             if (maxHeaderSize > 0)
             {
                 byte[] header = new byte[maxHeaderSize];
@@ -408,7 +408,7 @@ namespace ImageSharp
                 stream.Read(header, 0, maxHeaderSize);
                 stream.Position = 0;
 
-                IImageFormat format = Bootstrapper.ImageFormats.FirstOrDefault(x => x.Decoder.IsSupportedFileFormat(header));
+                IImageFormat format = Bootstrapper.ImageFormats.FirstOrDefault(x => x.IsSupportedFileFormat(header));
                 if (format != null)
                 {
                     format.Decoder.Decode(this, stream);

tests/ImageSharp.Tests/BootstrapperTests.cs

@@ -39,6 +39,10 @@ namespace ImageSharp.Tests
             public string Extension { get { return this.extension; } set { this.extension = value; } }
 
             public IEnumerable<string> SupportedExtensions { get { return this.supportedExtensions; } set { this.supportedExtensions = value; } }
+
+            public int HeaderSize { get { throw new NotImplementedException(); } }
+
+            public bool IsSupportedFileFormat(byte[] header) { throw new NotImplementedException(); }
         }
 
         [Fact]