图片无损缩放类（小弟初学，到低有没有损耗，还需高人指点）

using  System;
using  System.IO;
using  System.Drawing;
using  System.Drawing.Imaging;
using  System.Drawing.Drawing2D;

namespace  ZHT.Utility.Share
{
public   class  Thumbnail
{
    public  Thumbnail()
   {
   
   }   

    ///   <SUMMARY>
    ///  图片缩放
    ///   </SUMMARY>
    ///   <PARAM name="sourceFile"> 图片源路径 </PARAM>
    ///   <PARAM name="destFile"> 缩放后图片输出路径 </PARAM>
    ///   <PARAM name="destHeight"> 缩放后图片高度 </PARAM>
    ///   <PARAM name="destWidth"> 缩放后图片宽度 </PARAM>
    ///   <RETURNS></RETURNS>
         public   static   bool  GetThumbnail( string  sourceFile,  string  destFile,  int  destHeight,  int  destWidth)
        {
            System.Drawing.Image imgSource  =  System.Drawing.Image.FromFile(sourceFile);
            System.Drawing.Imaging.ImageFormat thisFormat  =  imgSource.RawFormat;
     int  sW  =   0 , sH  =   0 ; 
             //  按比例缩放
             int  sWidth  =  imgSource.Width;
             int  sHeight  =  imgSource.Height;

     if (sHeight > destHeight  ||  sWidth > destWidth)
    {
      if ((sWidth * destHeight) > (sHeight * destWidth))
     {
      sW  =  destWidth;
      sH  =  (destWidth * sHeight) / sWidth;
     }
      else
     {
      sH  =  destHeight;
      sW  =  (sWidth * destHeight) / sHeight;
     }
    }
     else
    {
     sW  =  sWidth;
     sH  =  sHeight;
    }

            Bitmap outBmp  =   new  Bitmap(destWidth, destHeight);
            Graphics g  =  Graphics.FromImage(outBmp);
    g.Clear(Color.WhiteSmoke);

             //  设置画布的描绘质量
            g.CompositingQuality  =  CompositingQuality.HighQuality; 
            g.SmoothingMode  =  SmoothingMode.HighQuality; 
            g.InterpolationMode  =  InterpolationMode.HighQualityBicubic;

            g.DrawImage(imgSource,  new  Rectangle((destWidth - sW) / 2 ,(destHeight - sH) / 2 , sW, sH), 0 , 0 , imgSource.Width, imgSource.Height, GraphicsUnit.Pixel);
            g.Dispose();

             //  以下代码为保存图片时，设置压缩质量
            EncoderParameters encoderParams  =   new  EncoderParameters();
             long [] quality  =   new   long [ 1 ];
            quality[ 0 ]  =   100 ;

            EncoderParameter encoderParam  =   new  EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
            encoderParams.Param[ 0 ]  =  encoderParam;

             try
            {
                 // 获得包含有关内置图像编码解码器的信息的ImageCodecInfo 对象。
                ImageCodecInfo[] arrayICI  =  ImageCodecInfo.GetImageEncoders();
                ImageCodecInfo jpegICI  =   null ;
                 for  ( int  x  =   0 ; x  <  arrayICI.Length; x ++ )
                {
                     if  (arrayICI[x].FormatDescription.Equals( " JPEG " ))
                    {
                        jpegICI  =  arrayICI[x]; // 设置JPEG编码
                         break ;
                    }
                }

                 if  (jpegICI  !=   null )
                {
                    outBmp.Save(destFile, jpegICI, encoderParams);
                }
                 else
                {
                    outBmp.Save(destFile, thisFormat);
                }

                 return   true ;
            }
             catch
            {
                 return   false ;
            }
             finally
            {
                imgSource.Dispose();
                outBmp.Dispose();
            }
        }
}
}