/引用命名空间
using System.Drawing.Imaging;
using System.Drawing;
using System.Drawing.Drawing2D;

#region GetPicThumbnail

    /// <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"></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 = 0, sH = 0;

        Size tem_size = new Size(iSource.Width, iSource.Height);

        if (tem_size.Width > dHeight || tem_size.Width > dWidth)

        {

            if ((tem_size.Width * dHeight) > (tem_size.Height * dWidth))

            {

                sW = dWidth;

                sH = (dWidth * tem_size.Height) / tem_size.Width;

            }

            else

            {

                sH = dHeight;

                sW = (tem_size.Width * dHeight) / tem_size.Height;

            }

        }

        else

        {

            sW = tem_size.Width;

            sH = tem_size.Height;

        }

        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();

        EncoderParameters ep = new EncoderParameters();

        long[] qy = new long[1];

        qy[0] = flag;

        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);

            }

            else

            {

                ob.Save(dFile, tFormat);

            }

            return true;

        }

        catch

        {

            return false;

        }

        finally

        {

            iSource.Dispose();

            ob.Dispose();

        }

    }

    #endregion