C#中不失真產生縮圖

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使用.net的方法GetThumbnailImage產生的縮圖失真嚴重，這裡推薦一種不失真產生縮圖的方法。

/// <summary>
/// 獲得縮微圖
/// </summary>
/// <returns></returns>
  public bool GetThumbImg()
{
try
{
string imgpath; //原始路徑
     if(imgsourceurl.IndexOf("\",0)<0) //使用的是相對路徑
     {
imgpath = HttpContext.Current.Server.MapPath(imgsourceurl); //轉化為實體路徑
     }
else
{
imgpath=imgsourceurl;
}
System.Drawing.Image sourceImage = System.Drawing.Image.FromFile(imgpath);
int width = sourceImage.Width;
int height = sourceImage.Height;
if(thumbwidth <= 0)
{
thumbwidth = 120;
}
if(thumbwidth >= width)
{
return false;
}
else
{
(thumbwidth,thHeight*thumbwidth/thWidth,null,IntPtr.Zero);
Image imgThumb=new System.Drawing.Bitmap(thumbwidth,height*thumbwidth/width);
System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(imgThumb);
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
g.DrawImage(sourceImage, new Rectangle(0, 0, thumbwidth,height*thumbwidth/width), 0, 0, width, height, GraphicsUnit.Pixel);
string thumbpath="";
sourceImage.Dispose();
if(thumburl=="")
{
thumbpath=imgpath;
}
if(thumbpath.IndexOf("\",0)<0)//使用的是相對路徑
      {
thumbpath=HttpContext.Current.Server.MapPath(thumburl);//轉化為實體路徑
      }
imgThumb.Save(thumbpath,ImageFormat.Jpeg);
imgThumb.Dispose();
return true;
}
}
catch
{
throw;
}
}