C#无损压缩图片

话不多说，请看代码：

/// <summary>
    /// 根据指定尺寸得到按比例缩放的尺寸,返回true表示以更改尺寸
    /// </summary>
    /// <param name="picWidth">图片宽度</param>
    /// <param name="picHeight">图片高度</param>
    /// <param name="specifiedWidth">指定宽度</param>
    /// /// <param name="specifiedHeight">指定高度</param>
    /// <returns>返回true表示以更改尺寸</returns>
    private bool GetPicZoomSize(ref int picWidth, ref int picHeight, int specifiedWidth, int specifiedHeight)
    {
      int sW = 0, sH = 0;
      Boolean isZoomSize = false;
      //按比例缩放
      Size tem_size = new Size(picWidth, picHeight);
      if (tem_size.Width > specifiedWidth || tem_size.Height > specifiedHeight) //将**改成c#中的或者操作符号
      {
        if ((tem_size.Width * specifiedHeight) > (tem_size.Height * specifiedWidth))
        {
          sW = specifiedWidth;
          sH = (specifiedWidth * tem_size.Height) / tem_size.Width;
        }
        else
        {
          sH = specifiedHeight;
          sW = (tem_size.Width * specifiedHeight) / tem_size.Height;
        }
        isZoomSize = true;
      }
      else
      {
        sW = tem_size.Width;
        sH = tem_size.Height;
      }
      picHeight = sH;
      picWidth = sW;
      return isZoomSize;
    }
    /// <summary>
    /// 无损压缩图片
    /// </summary>
    /// <param name="sFile">原图片</param>
    /// <param name="dFile">压缩后保存位置</param>
    /// <param name="dHeight">高度</param>
    /// <param name="dWidth">宽度</param>
    /// <param name="flag">压缩质量 1-100</param>
    /// <returns></returns>

    public bool GetPicThumbnail(string sFile, string dFile, int dHeight, int dWidth, int flag)
    {
      System.Drawing.Image iSource = System.Drawing.Image.FromFile(sFile);
      ImageFormat tFormat = iSource.RawFormat;
      int sW = iSource.Width, sH = iSource.Height;

      GetPicZoomSize(ref sW, ref sH, dWidth, dHeight);

      Bitmap ob = new Bitmap(dWidth, dHeight);
      Graphics g = Graphics.FromImage(ob);
      g.Clear(Color.WhiteSmoke);
      g.CompositingQuality = CompositingQuality.HighQuality;
      g.SmoothingMode = SmoothingMode.HighQuality;
      g.InterpolationMode = InterpolationMode.HighQualityBicubic;
      g.DrawImage(iSource, new Rectangle((dWidth - sW) / 2, (dHeight - sH) / 2, sW, sH), 0, 0, iSource.Width, iSource.Height, GraphicsUnit.Pixel);
      g.Dispose();
      //以下代码为保存图片时，设置压缩质量
      EncoderParameters ep = new EncoderParameters();
      long[] qy = new long[1];
      qy[0] = flag;//设置压缩的比例1-100
      EncoderParameter eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
      ep.Param[0] = eParam;
      try
      {
        ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();

        ImageCodecInfo jpegICIinfo = null;

        for (int x = 0; x < arrayICI.Length; x++)
        {
          if (arrayICI[x].FormatDescription.Equals("JPEG"))
          {
            jpegICIinfo = arrayICI[x];
            break;
          }
        }
        if (jpegICIinfo != null)
        {
          ob.Save(dFile, jpegICIinfo, ep);//dFile是压缩后的新路径
        }
        else
        {
          ob.Save(dFile, tFormat);
        }
        return true;
      }
      catch
      {
        return false;
      }
      finally
      {
        iSource.Dispose();
        ob.Dispose();
      }
    }

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