asp.net 图片超过指定大小后等比例压缩图片的方法

/// <summary>

        /// 压缩图片

        /// </summary>

        /// <returns></returns>

        public string ResizePic()

        {

            #region 压缩图片开始

            bool IsImgFile = true;  //判断是否为图片文件

            string filePathName = "123";   //文件存储的路径（文件夹名称）

            string fileName = "a.jpg";   //上传文件的原始名称

            string fileSysName = DateTime.Now.ToString("yyyyMMddHHmmssfff") + "_" + fileName;  //修改后的文件名称

            string filePath = "";   //文件路径

            string strImgPath = "/fileupload/";   //上传路径

            if (IsImgFile)

            {

                int maxWidth = 600;   //图片宽度最大限制

                int maxHeight = 400;  //图片高度最大限制

                System.Drawing.Image imgPhoto =

                    System.Drawing.Image.FromFile(Server.MapPath(strImgPath) + filePathName + "/" + fileSysName);

                int imgWidth = imgPhoto.Width;

                int imgHeight = imgPhoto.Height;

                if (imgWidth > imgHeight)  //如果宽度超过高度以宽度为准来压缩

                {

                    if (imgWidth > maxWidth)  //如果图片宽度超过限制

                    {

                        float toImgWidth = maxWidth;   //图片压缩后的宽度

                        float toImgHeight = imgHeight / (float)(imgWidth / toImgWidth); //图片压缩后的高度

                        System.Drawing.Bitmap img = new System.Drawing.Bitmap(imgPhoto,
                                                                              int.Parse(toImgWidth.ToString()),
                                                                              int.Parse(toImgHeight.ToString()));
                        string strResizePicName = Server.MapPath(strImgPath) + filePathName + "/_small_" + fileSysName;
                        img.Save(strResizePicName);  //保存压缩后的图片
                        filePath = strImgPath + filePathName + "/_small_" + fileSysName;  //返回压缩后的图片路径
                    }
                }
                else
                {
                    if (imgHeight > maxHeight)
                    {
                        float toImgHeight1 = maxHeight;
                        float toImgWidth1 = imgWidth / (float)(imgHeight / toImgHeight1);

                        System.Drawing.Bitmap img = new System.Drawing.Bitmap(imgPhoto,
                                                                              int.Parse(toImgWidth1.ToString()),
                                                                              int.Parse(toImgHeight1.ToString()));
                        string strResizePicName = Server.MapPath(strImgPath) + filePathName + "/_small_" + fileSysName;
                        img.Save(strResizePicName);
                        filePath = strImgPath + filePathName + "/_small_" + fileSysName;
                    }
                }
            }
            return filePath;
            #endregion
        }