C#如何批量修改图片尺寸和DPI

string[] filedir = Directory.GetFiles(Root, "*.png", SearchOption.AllDirectories);

        private void button1_Click(object sender, EventArgs e)
        {
            string Root = this.textBox1.Text.Trim();
 
            // 读取文件夹下的所有文件 （方法一）
            string[] filedir = Directory.GetFiles(Root, "*", SearchOption.AllDirectories);
            foreach (string fileName in filedir)
            {
                ChagePicDPI(fileName);
            }
 
             方法二
            //DirectoryInfo folder = new DirectoryInfo(Root);
            //foreach (FileInfo file in folder.GetFiles("*"))
            //{
            //    // 修改图片dpi
            //    ChagePicDPI(file);
            //}
            MessageBox.Show("ok");
        }
 
        private void ChagePicDPI(string fileName)
        {
            int newWidth = 400;   // 固定图像宽度
            int DPI = 1200;    // 图像DPI             
 
            using (Bitmap oldBitmap = new Bitmap(fileName))
            {
                int newHeight = Convert.ToInt32(1.0 * oldBitmap.Height * newWidth / oldBitmap.Width);   //  图像高度按照宽度等比变化
 
                using (Bitmap newBitmap = new Bitmap(newWidth, newHeight, PixelFormat.Format24bppRgb))
                {
                    using (Graphics g = Graphics.FromImage(newBitmap))
                    {
                        g.Clear(System.Drawing.Color.White);  // 背景白色
                        g.DrawImage(oldBitmap, new Rectangle(0, 0, newBitmap.Width, newBitmap.Height));
                        newBitmap.SetResolution(DPI, DPI);  // 设置DPI
 
                        string newFileName = fileName.Replace("D:\\图形", "C:\\Users\\Administrator\\Desktop\\11111");  // 替换文件路径
                        string dir = Path.GetDirectoryName(newFileName);
                        if (!Directory.Exists(dir))
                        {
                            Directory.CreateDirectory(dir);
                        }
 
                        newBitmap.Save(newFileName, oldBitmap.RawFormat);   // 保存图片，按照图片原始格式保存
                    }
                }
            }
        }