How to convert Bitmap to a Base64 string?

I'm trying to capture the screen and then convert it to a Base64 string. This is my code:

Rectangle bounds = Screen.GetBounds(Point.Empty);
Bitmap bitmap = new Bitmap(bounds.Width, bounds.Height);

using (Graphics g = Graphics.FromImage(bitmap))
{
   g.CopyFromScreen(Point.Empty, Point.Empty, bounds.Size);
}

// Convert the image to byte[]
System.IO.MemoryStream stream = new System.IO.MemoryStream();
bitmap.Save(stream, System.Drawing.Imaging.ImageFormat.Bmp);
byte[] imageBytes = stream.ToArray();

// Write the bytes (as a string) to the textbox
richTextBox1.Text = System.Text.Encoding.UTF8.GetString(imageBytes);

// Convert byte[] to Base64 String
string base64String = Convert.ToBase64String(imageBytes);

Using a richTextBox to debug, it shows:

BM6�~

So for some reason the bytes aren't correct which causes the base64String to become null. Any idea what I'm doing wrong? Thanks.

I found a solution for my issue:

Bitmap bImage = newImage;  // Your Bitmap Image
System.IO.MemoryStream ms = new MemoryStream();
bImage.Save(ms, ImageFormat.Jpeg);
byte[] byteImage = ms.ToArray();
var SigBase64= Convert.ToBase64String(byteImage); // Get Base64

The characters you get by doing System.Text.Encoding.UTF8.GetString(imageBytes) will (almost certainly) contain unprintable characters. This could cause you to only see those few characters. If you first convert it to a base64-string, then it will contain only printable characters and can be shown in a text box:

// Convert byte[] to Base64 String
string base64String = Convert.ToBase64String(imageBytes);

// Write the bytes (as a Base64 string) to the textbox
richTextBox1.Text = base64String;

No need for byte[] ...just convert the stream directly (w/using constructs)

using (var ms = new MemoryStream())
{    
  using (var bitmap = new Bitmap(newImage))
  {
    bitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
    var SigBase64= Convert.ToBase64String(ms.GetBuffer()); //Get Base64
  }
}