C# Bitmap实现图片按比例或固定尺寸缩放

/// <summary>
        /// C#图片缩放
        /// </summary>
        /// <param name="strFile">原文件完整名称</param>
        /// <param name="strNewFile">新文件完整名称</param>
        /// <param name="intWidth">新的宽度</param>
        /// <param name="intHeight">新的高度(若高度为0, 按比例缩放)</param>
        /// <returns></returns>
        public static bool picResize(string strFile, string strNewFile, int intWidth, int intHeight)
        {
            System.Drawing.Bitmap objPic, objNewPic;
            try
            {
                if (!File.Exists(strFile))
                    return false;
                objPic = new System.Drawing.Bitmap(strFile);
                if (intHeight <= 0)
                    intHeight = (intWidth * objPic.Height / objPic.Width);
                objNewPic = new System.Drawing.Bitmap(objPic, intWidth, intHeight);
                objPic.Dispose();
                objPic = null;
                string newFile = strNewFile.Substring(0, strNewFile.LastIndexOf('.'));
                //格式可以截取图片的后缀，再判断文件格式
                objNewPic.Save(newFile + ".jpg", ImageFormat.Jpeg);
                objNewPic.Dispose();
                File.Delete(strFile);

            }
            catch (Exception ex)
            {