Base64是网络上最常见的用于传输8Bit字节码的编码方式之一，Base64就是一种基于64个可打印字符来表示二进制数据的方法。可查看RFC2045～RFC2049，上面有MIME的详细规范。
Base64编码是从二进制到字符的过程，可用于在HTTP环境下传递较长的标识信息。采用Base64编码具有不可读性，需要解码后才能阅读。
Base64由于以上优点被广泛应用于计算机的各个领域，然而由于输出内容中包括两个以上“符号类”字符（ , /, =)，不同的应用场景又分别研制了Base64的各种“变种”。为统一和规范化Base64的输出，Base62x被视为无符号化的改进版本。
图片转BASE64
代码语言：javascript复制 ''' <summary>
''' 图片转BASE64
''' </summary>
''' <param name="IMG">要转换的图片</param>
''' <returns></returns>
Function IMG_TO_BASE64(ByVal IMG As Image) As String
Try
If Not IsNothing(IMG) Then
Dim MS As New IO.MemoryStream()
Using BMP As New Bitmap(IMG)
BMP.Save(MS, Imaging.ImageFormat.Jpeg)
Dim BYT As Byte() = MS.GetBuffer()
Dim Base64_Str As String = Convert.ToBase64String(BYT)
Return Base64_Str
End Using
Else
Return "没有要转换的图片"
End If
Catch ex As Exception
Return ex.Message
End Try
End Function
BASE64转图片
代码语言：javascript复制 ''' <summary>
''' BASE64转图片
''' </summary>
''' <param name="BASE_STR">BASE64数据</param>
''' <returns></returns>
Function BASE64_TO_IMG(ByVal BASE_STR As String) As Image
Try
Dim IMG As Image
If BASE_STR <> Nothing And Strings.Right(BASE_STR, 1) = "=" Then
Dim BYT As Byte() = Convert.FromBase64String(BASE_STR)
Dim MS As New IO.MemoryStream(BYT)
IMG = Image.FromStream(MS)
Return IMG
Else
Return Nothing
End If
Catch ex As Exception
Return Nothing
End Try
End Function
根据字符串计算图片转换后文件大小
代码语言：javascript复制 ''' <summary>
''' 根据字符串计算txt文件大小
''' </summary>
''' <param name="picstr">字符串</param>
''' <returns></returns>
Function PIC_LENG(ByVal picstr As String) As Double
Try
Dim bytes As Byte() = System.Text.Encoding.ASCII.GetBytes(picstr)
Dim Length As Integer = bytes.Length
Return Math.Round(Length / 1024 / 1024, 2)
Catch ex As Exception
Return 0
End Try
End Function
