c# 图片按比例缩放

public static Bitmap GetThumbnail(Bitmap b, int destHeight,int destWidth)           {                       System.Drawing.Image imgSource = b;                  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.Transparent);                     // 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;               imgSource.Dispose();                     return outBmp;              }