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Convert an image to a Base64 string and vice versa

dec 19

Geplaatst door: André Obelink (Host)
19-12-2008 22:30

In some cases you want to convert an image to a string which can be stored in for example a XML file. Once the string is stored as simple text, you want also be able to convert these readable characters back to the original image. Fortunately this is very easy to achieve with classes from the .NET platform. The trick is to use a MemoryStream and save an image to it. Then convert the result of MemoryStream.ToArray() to a Base64 string. Retrieving the image back from the Base64 string is even more easy. Create a MemoryStream based on that string and use the Image.FromStream() method to get the original image. In this example I create a class, named ImageHelper. In this class I define the two methods: ImageToBase64String() and ImageFrom64BaseString(). By using the Base64 format you are sure that the result string will not contain any characters which will be corrupt your XML file, like a '<' or '>'.

   1: Imports System.IO

   2: Imports System.Drawing.Imaging

3:

   4: Public Class ImageHelper

5:

   6:     ' Convert an image to a Base64 string by using a MemoryStream. Save the

   7:     ' image to the MemoryStream and use Convert.ToBase64String to convert

   8:     ' the content of that MemoryStream to a Base64 string.

   9:     Public Shared Function ImageToBase64String(ByVal image As Image, _

  10:                                                ByVal imageFormat As ImageFormat)

11:

  12:         Using memStream As New MemoryStream

13:

  14:             image.Save(memStream, imageFormat)

15:

  16:             Dim result As String = Convert.ToBase64String(memStream.ToArray())

17:

  18:             memStream.Close()

19:

  20:             Return result

21:

  22:         End Using

23:

  24:     End Function

25:

  26:     ' Convert a Base64 string back to an image. Fill a MemorySTream based

  27:     ' on the Base64 string and call the Image.FromStream() methode to

  28:     ' convert the content of the MemoryStream to an image.

  29:     Public Shared Function ImageFromBase64String(ByVal base64 As String)

30:

  31:         Using memStream As New MemoryStream(Convert.FromBase64String(base64))

32:

  33:             Dim result As Image = Image.FromStream(memStream)

34:

  35:             memStream.Close()

36:

  37:             Return result

38:

  39:         End Using

40:

  41:     End Function

42:

  43: End Class

As you can see I have defined both methods as so called Shared methods. When using these Shared methods you are not forced to instantiate the class. You can simply use the method by calling the ClassName.MethodName(). In the code example below you can see how easy it is to convert an image to a Base64 string and vice versa.

   1: Imports System.Drawing.Imaging

2:

3:

   4: Private Sub ImageToBase64StringButton_Click() Handles ImageToBase64Button.Click

5:

   6:     ' Convert the original image to a Base64 string

   7:     Base64TextBox.Text = ImageHelper.ImageToBase64String(SourcePictureBox.Image, _

   8:                                                          ImageFormat.Jpeg)

9:

  10: End Sub

11:

  12: Private Sub ImageFromBase64StringButton_Click() Handles ImageFromBase64Button.Click

13:

  14:     ' Convert a Base64 string to the original image

  15:     TargetPictureBox.Image = ImageHelper.ImageFromBase64String(Base64TextBox.Text)

16:

  17: End Sub

To give you some idea how this code works... see the screen shot below..

Happy coding!

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