Change filter method signature

src/ImageSharp/Formats/Png/Filters/AverageFilter.cs

@@ -20,13 +20,9 @@ namespace ImageSharp.Formats
         /// <param name="scanline">The scanline to decode</param>
         /// <param name="previousScanline">The previous scanline.</param>
         /// <param name="bytesPerPixel">The bytes per pixel.</param>
-        /// <returns>
-        /// The <see cref="T:byte[]"/>
-        /// </returns>
-        public static byte[] Decode(byte[] scanline, byte[] previousScanline, int bytesPerPixel)
+        public static void Decode(byte[] scanline, byte[] previousScanline, int bytesPerPixel)
         {
             // Average(x) + floor((Raw(x-bpp)+Prior(x))/2)
-
             fixed (byte* scan = scanline)
             fixed (byte* prev = previousScanline)
             {
@@ -38,8 +34,6 @@ namespace ImageSharp.Formats
                     scan[x] = (byte)((scan[x] + Average(left, above)) % 256);
                 }
             }
-
-            return scanline;
         }
 
         /// <summary>

src/ImageSharp/Formats/Png/Filters/PaethFilter.cs

@@ -21,11 +21,9 @@ namespace ImageSharp.Formats
         /// <param name="scanline">The scanline to decode</param>
         /// <param name="previousScanline">The previous scanline.</param>
         /// <param name="bytesPerPixel">The bytes per pixel.</param>
-        /// <returns>The <see cref="T:byte[]"/></returns>
-        public static byte[] Decode(byte[] scanline, byte[] previousScanline, int bytesPerPixel)
+        public static void Decode(byte[] scanline, byte[] previousScanline, int bytesPerPixel)
         {
             // Paeth(x) + PaethPredictor(Raw(x-bpp), Prior(x), Prior(x-bpp))
-
             fixed (byte* scan = scanline)
             fixed (byte* prev = previousScanline)
             {
@@ -38,8 +36,6 @@ namespace ImageSharp.Formats
                     scan[x] = (byte)((scan[x] + PaethPredicator(left, above, upperLeft)) % 256);
                 }
             }
-
-            return scanline;
         }
 
         /// <summary>

src/ImageSharp/Formats/Png/Filters/SubFilter.cs

@@ -18,7 +18,7 @@ namespace ImageSharp.Formats
         /// <param name="scanline">The scanline to decode</param>
         /// <param name="bytesPerPixel">The bytes per pixel.</param>
         /// <returns>The <see cref="T:byte[]"/></returns>
-        public static byte[] Decode(byte[] scanline, int bytesPerPixel)
+        public static void Decode(byte[] scanline, int bytesPerPixel)
         {
             // Sub(x) + Raw(x-bpp)
             fixed (byte* scan = scanline)
@@ -29,8 +29,6 @@ namespace ImageSharp.Formats
                     scan[x] = (byte)((scan[x] + priorRawByte) % 256);
                 }
             }
-
-            return scanline;
         }
 
         /// <summary>

src/ImageSharp/Formats/Png/Filters/UpFilter.cs

@@ -17,8 +17,7 @@ namespace ImageSharp.Formats
         /// </summary>
         /// <param name="scanline">The scanline to decode</param>
         /// <param name="previousScanline">The previous scanline.</param>
-        /// <returns>The <see cref="T:byte[]"/></returns>
-        public static byte[] Decode(byte[] scanline, byte[] previousScanline)
+        public static void Decode(byte[] scanline, byte[] previousScanline)
         {
             // Up(x) + Prior(x)
             fixed (byte* scan = scanline)
@@ -31,8 +30,6 @@ namespace ImageSharp.Formats
                     scan[x] = (byte)((scan[x] + above) % 256);
                 }
             }
-
-            return scanline;
         }
 
         /// <summary>
@@ -42,7 +39,6 @@ namespace ImageSharp.Formats
         /// <param name="previousScanline">The previous scanline.</param>
         /// <param name="result">The filtered scanline result.</param>
         /// <param name="bytesPerScanline">The number of bytes per scanline</param>
-        /// <returns>The <see cref="T:byte[]"/></returns>
         public static void Encode(byte[] scanline, byte[] previousScanline, byte[] result, int bytesPerScanline)
         {
             // Up(x) = Raw(x) - Prior(x)