public Bitmap ConvertToGrayscale(Bitmap source)
{
  Bitmap bm = new Bitmap(source.Width,source.Height);
  for(int y=0;y<bm.Height;y++)
  {
    for(int x=0;x<bm.Width;x++)
    {
      Color c=source.GetPixel(x,y);
      int luma = (int)(c.R*0.3 + c.G*0.59+ c.B*0.11);
      bm.SetPixel(x,y,Color.FromArgb(luma,luma,luma));
    }
  }
  return bm;
}