asp.net上传图片文件自动修改图片大小代码

  #region 图片缩放
      /// <summary>
        /// 图片缩放
      /// </summary>
      /// <param name="savePath">图片相对路径</param>
      /// <param name="fileName">图片名称</param>
      /// <param name="destWidth">缩放宽度</param>
      /// <param name="destHeight">高度</param>
       /// <param name="type">1--固定缩放；2--按比例缩放；3--指定宽度,宽度大于指定宽度按指定宽度进行等比缩放，小于指定宽度按原图大小上传；4--原图直接上传</param>
       /// <returns></returns>
        public static void ReducesPic(string savePath,string fileName, int destWidth, int destHeight, int type)
        {
            if (!fileName.Equals(""))
            {
                string Allpath = System.Web.HttpContext.Current.Server.MapPath("/") + savePath;
                //生成原图
                System.IO.Stream stream = System.IO.File.OpenRead(Allpath + fileName);
                System.Drawing.Image oImage = System.Drawing.Image.FromStream(stream);
                stream.Close();
                stream.Dispose();

                System.Drawing.Image.GetThumbnailImageAbort callb = new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback);

                string fileType = fileName.Substring(fileName.LastIndexOf(".") + 1);
                int oWidth = oImage.Width;
                int oHeight = oImage.Height;

                int tWidth = destWidth; //设置缩略图初始宽度
                int tHeight = destHeight; //设置缩略图初始高度

                //按指定宽高缩放
                if (type == 1)
                {
                    tWidth = destWidth;
                    tHeight = destHeight;
                }
                //按比例计算出缩略图的宽度和高度
                else if (type == 2)
                {
                    if (oWidth > tWidth || oHeight > tHeight)
                    {
                        if (oWidth >= oHeight)
                        {
                            tHeight = (int)Math.Floor(Convert.ToDouble(oHeight) * (Convert.ToDouble(tWidth) / Convert.ToDouble(oWidth)));
                        }
                        else
                        {
                            tWidth = (int)Math.Floor(Convert.ToDouble(oWidth) * (Convert.ToDouble(tHeight) / Convert.ToDouble(oHeight)));
                        }
                    }
                    else
                    {
                        tWidth = oWidth; //原图宽度
                        tHeight = oHeight; //原图高度
                    }
                }
                //指定宽度,宽度大于指定宽度按指定宽度进行等比缩放，小于指定宽度按原图大小上传
                else if (type == 3)
                {
                    if (oWidth >= tWidth)
                    {
                        if (oWidth >= oHeight)
                        {
                            tHeight = (int)Math.Floor(Convert.ToDouble(oHeight) * (Convert.ToDouble(tWidth) / Convert.ToDouble(oWidth)));
                        }
                        else
                        {
                            tWidth = (int)Math.Floor(Convert.ToDouble(oWidth) * (Convert.ToDouble(tHeight) / Convert.ToDouble(oHeight)));
                        }
                    }
                    else
                    {
                        tWidth = oWidth; //原图宽度
                        tHeight = oHeight; //原图高度
                    }

                }
                else
                {
                    tWidth = oWidth; //原图宽度
                    tHeight = oHeight; //原图高度
                }
                //生成缩略原图
                oImage = oImage.GetThumbnailImage(tWidth, tHeight, callb, IntPtr.Zero);
                oImage.Save(Allpath+fileName);

            }

        }
        public static bool ThumbnailCallback() { return false; }
        #endregion