asp.net 图片超过指定大小后等比例压缩图片的方法

                        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;