高質量圖片無損壓縮算法

朋友開了網店，想讓我幫忙作一些小工具，其中就包含了圖片無損壓縮的需求，這一類的軟件和代碼在網上有不少，可是真正實用的符合本身定製化需求的沒幾個，因而就想着本身DIY一下（本身動手豐衣足食^o^），並貼出核心代碼供你們學習和參考

        /// <summary>
        /// 無損壓縮圖片
        /// </summary>
        /// <param name="sFile">原圖片地址</param>
        /// <param name="dFile">壓縮後保存圖片地址</param>
        /// <param name="flag">壓縮質量（數字越小壓縮率越高）1-100</param>
        /// <returns></returns>
        public static bool CompressImage(string sFile, string dFile, int flag = 90)
        {
            Image iSource = Image.FromFile(sFile);
            ImageFormat tFormat = iSource.RawFormat;

            int dHeight = iSource.Height / 2;
            int dWidth = iSource.Width / 2;
            int sW, sH;
            //按比例縮放
            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.Width * 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();

            //如下代碼爲保存圖片時，設置壓縮質量
            EncoderParameters ep = new EncoderParameters();
            long[] qy = new long[1];
            qy[0] = flag;//設置壓縮的比例1-100
            EncoderParameter eParam = new EncoderParameter(Encoder.Quality, qy);
            ep.Param[0] = eParam;

            try
            {
                ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
                ImageCodecInfo jpegICIinfo = arrayICI.FirstOrDefault(t => t.FormatDescription.Equals("JPEG"));
                if (jpegICIinfo != null)
                {
                    ob.Save(dFile, jpegICIinfo, ep);//dFile是壓縮後的新路徑
                }
                else
                {
                    ob.Save(dFile, tFormat);
                }
                return true;
            }
            catch
            {
                return false;
            }
            finally
            {
                iSource.Dispose();
                ob.Dispose();
            }
        }