Private Shared Function Bildformat(ByVal File As String) As _
      Drawing.Imaging.ImageFormat
 
        File = Trim(UCase(File))
        If Len(File) < 5 Then
            Return Drawing.Imaging.ImageFormat.Bmp
        End If
 
        Dim ext3 As String = Right(File, 4)
        Dim ext4 As String = Right(File, 5)
 
        If ext3 = ".JPG" Or ext3 = ".JPE" Or _
          ext4 = ".JPEG" Or ext4 = ".JFIF" Then
            Return Drawing.Imaging.ImageFormat.Jpeg
        ElseIf ext3 = ".TIF" Or ext4 = ".TIFF" Then
            Return Drawing.Imaging.ImageFormat.Tiff
        ElseIf ext3 = ".PNG" Then
            Return Drawing.Imaging.ImageFormat.Png
        ElseIf ext3 = ".GIF" Then
            Return Drawing.Imaging.ImageFormat.Gif
        Else
            ' sonst: (BMP, DIB, RLE)
            Return Drawing.Imaging.ImageFormat.Bmp
        End If
    End Function
 
    Private Shared Sub ByteSector(ByVal val As Byte, ByVal length As Byte,
                                  ByRef minval As Byte, ByRef maxval As Byte)
        minval = CByte(Math.Max(CInt(val) - length, 0))
        maxval = CByte(Math.Min(CInt(val) + length, 255))
    End Sub