Using MemoryMarshal.AsBytes in Write8BitGray to get the bytes of a row

src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Buffers;
 using System.IO;
+using System.Runtime.InteropServices;
 
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Common.Helpers;
@@ -389,17 +390,10 @@ namespace SixLabors.ImageSharp.Formats.Bmp
 
             stream.Write(colorPalette);
 
-            using (IMemoryOwner<byte> rowSpanBuffer = this.memoryAllocator.AllocateManagedByteBuffer(image.Width, AllocationOptions.Clean))
-            {
-                Span<byte> outputPixelRow = rowSpanBuffer.GetSpan();
             for (int y = image.Height - 1; y >= 0; y--)
             {
-                    Span<TPixel> inputPixelRow = image.GetPixelRowSpan(y);
+                ReadOnlySpan<TPixel> inputPixelRow = image.GetPixelRowSpan(y);
-                    PixelOperations<TPixel>.Instance.ToGray8Bytes(
+                ReadOnlySpan<byte> outputPixelRow = MemoryMarshal.AsBytes(inputPixelRow);
-                        this.configuration,
-                        inputPixelRow,
-                        outputPixelRow,
-                        image.Width);
                 stream.Write(outputPixelRow);
 
                 for (int i = 0; i < this.padding; i++)
@@ -410,4 +404,3 @@ namespace SixLabors.ImageSharp.Formats.Bmp
         }
     }
 }
-}