Do you remove the data:image/jpeg;base64, before decoding Base64 string using C#?

Question

I'm trying to convert a Base64 encoded string that was generated from a re-sized image from the canvas element and I'm getting the following error when converting using the Convert.FromBase64()

The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or an illegal character among the padding characters.

The encoded data looks like this to start and ends with the =

data:image/jpeg;base64,/...=

What I don't quite understand is when I perform the Convert.FromBase64() do I need to strip off the prefix of data:image/jpeg;base64, and then decode the remainder?

The code I'm using to decode this is like below

string base64String = newinput.Value.ToString();

// Convert Base64 String to byte[]
byte[] imageBytes = Convert.FromBase64String(base64String);
MemoryStream ms = new MemoryStream(imageBytes, 0, imageBytes.Length);


// Convert byte[] to Image
ms.Write(imageBytes, 0, imageBytes.Length);
System.Drawing.Image image = System.Drawing.Image.FromStream(ms, true);

string newFile = Guid.NewGuid().ToString() + ".jpg";
image.Save(Path.Combine(Server.MapPath("~/Assets/") + Request.QueryString["id"] + "/", newFile), ImageFormat.Jpeg);

Basically, I'm converted the string into the image and saving on the server. As you can see I'm using C#

Any ideas?

Answer 1

do I need to strip off the prefix of data:image/jpeg;base64, and then decode the remainder?

Yes - the prefix isn't base64-encoded text, it's just saying that the rest is base64-encoded (and what the mime-type is).

We don't know exactly how you're obtaining the data, but you should check that the data URL is claiming to be base64 encoded first, mind.