C#实现为一张大尺寸图片创建缩略图的方法

public static Bitmap CreateThumbnail(string lcFilename, int lnWidth, int lnHeight)
{
  System.Drawing.Bitmap bmpOut = null;
  try
  {
    Bitmap loBMP = new Bitmap(lcFilename);
    ImageFormat loFormat = loBMP.RawFormat;
    decimal lnRatio;
    int lnNewWidth = 0;
    int lnNewHeight = 0;
    //*** If the image is smaller than a thumbnail just return it
    if (loBMP.Width < lnWidth && loBMP.Height < lnHeight)
      return loBMP;
    if (loBMP.Width > loBMP.Height)
    {
      lnRatio = (decimal)lnWidth / loBMP.Width;
      lnNewWidth = lnWidth;
      decimal lnTemp = loBMP.Height * lnRatio;
      lnNewHeight = (int)lnTemp;
    }
    else
    {
      lnRatio = (decimal)lnHeight / loBMP.Height;
      lnNewHeight = lnHeight;
      decimal lnTemp = loBMP.Width * lnRatio;
      lnNewWidth = (int)lnTemp;
    }
    bmpOut = new Bitmap(lnNewWidth, lnNewHeight);
    Graphics g = Graphics.FromImage(bmpOut);
    g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
    g.FillRectangle(Brushes.White, 0, 0, lnNewWidth, lnNewHeight);
    g.DrawImage(loBMP, 0, 0, lnNewWidth, lnNewHeight);
    loBMP.Dispose();
  }
  catch
  {
    return null;
  }
  return bmpOut;
}