Added method to reset the pixels of the PixelAccessor or PixelRow.

src/ImageSharp/Image/PixelAccessor.cs

@@ -399,5 +399,13 @@ namespace ImageSharp
         {
             return this.pixelsBase + ((targetY * this.Width) * Unsafe.SizeOf<TColor>());
         }
+
+        /// <summary>
+        /// Resets all the pixels to it's initial value.
+        /// </summary>
+        internal void Reset()
+        {
+            Unsafe.InitBlock(this.pixelsBase, 0, (uint)(this.RowStride * this.Height));
+        }
     }
 }

src/ImageSharp/Image/PixelRow.cs

@@ -7,6 +7,7 @@ namespace ImageSharp
 {
     using System;
     using System.IO;
+    using System.Runtime.CompilerServices;
     using System.Runtime.InteropServices;
 
     /// <summary>
@@ -201,5 +202,13 @@ namespace ImageSharp
 
             throw new NotSupportedException();
         }
+
+        /// <summary>
+        /// Resets the bytes of the array to it's initial value.
+        /// </summary>
+        internal void Reset()
+        {
+            Unsafe.InitBlock(this.PixelBase, 0, (uint)this.Bytes.Length);
+        }
     }
 }