Fast Greyscale using unsafe code in C#

/*
  Fast Greyscale using unsafe code in C#
  --
  Insert this as a function anywere, I used it in a seperate DLL
  to keep my form code clean.  Just pass the Bitmap and the picture
  box to show it in to the function

  If anyone has tried using the .NET Graphics API, they know that
  replacing pixel colors takes a long time to complete. I did some
  research and found a good source. This code will adjust the color
  to greyscale by Binary.
  The page is http://www.navicosoft.com/software_articles/softwares_articles_index.html
  for more information. It is under Basic Image Processing in the
  list of articles.
*/

public void greyscale(Bitmap bmp, PictureBox picBox)
{
       BitmapData data = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height),
           ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
       unsafe
       {
           byte* imgPtr = (byte*)(data.Scan0);
           byte red, green, blue;
           for (int i = 0; i < data.Height; i++)
           {
               for (int j = 0; j < data.Width; j++)
               {
                   blue = imgPtr[0];
                   green = imgPtr[1];
                   red = imgPtr[2];

                   imgPtr[0] = imgPtr[1] = imgPtr[2] =
                      (byte)(.299 * red
                       + .587 * green
                       + .114 * blue);
                   imgPtr += 3;
               }
               imgPtr += data.Stride - data.Width * 3;
           }

       }
       bmp.UnlockBits(data);
       picBox.Image = bmp;
}