/// <summary>
        /// 图片缩放   无水印
        /// </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);
           

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