C#把图片转为base64

public static Image UrlToImage(string url)
{
try
{
WebClient mywebclient = new WebClient();
byte[] Bytes = mywebclient.DownloadData(url);
using (MemoryStream ms = new MemoryStream(Bytes))
{
Image outputImg = Image.FromStream(ms);
return outputImg;
}
}
catch (Exception ex)
{
return null;
}
}

public static string ImageToBase64(Image img)
{
try
{
Bitmap bmp = new Bitmap(img);
MemoryStream ms = new MemoryStream();
bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
byte[] arr = new byte[ms.Length];
ms.Position = 0;
ms.Read(arr, 0, (int)ms.Length);
ms.Close();
return Convert.ToBase64String(arr);
}
catch (Exception ex)
{
return null;
}
}