How save image by using bound of stroke in WPF?

Question

I made a paint application. It can create line, rectangle and can add annotation on image. All element is Stroke which be drawn in InkCanvas. This canvas will be expand to fit screen. But if I want to save image, I don't want to save full size of inkcanvas. But I want to save by using bounds of each stroke. (min left, min top, max right,max bottom)

   Private Function GetMaxBound() As Windows.Rect
    Dim maxLeft As Integer = 10000
    Dim maxTop As Integer = 10000
    Dim maxRight As Integer = 0
    Dim maxBottom As Integer = 0
    For Each s As Windows.Ink.Stroke In m_inkCanvas.Strokes
        Dim bound As Windows.Rect = s.GetBounds
        If bound.Left < maxLeft Then
            maxLeft = bound.Left
        End If
        If bound.Top < maxTop Then
            maxTop = bound.Top
        End If
        If bound.Right > maxRight Then
            maxRight = bound.Right
        End If
        If bound.Bottom > maxBottom Then
            maxBottom = bound.Bottom
        End If
    Next
    Dim width As Integer = Math.Abs(maxRight - maxLeft)
    Dim height As Integer = Math.Abs(maxTop - maxBottom)
    Return New Windows.Rect(maxLeft, maxTop, width, height)
End Function

I try to use these function

 Private Function SaveImage(ByVal targetPath As String) As Boolean
    'Dim rect As Windows.Rect = GetMaxBound()
    'Dim width As Double = rect.Width
    'Dim height As Double = rect.Height
    Dim width As Double = m_inkCanvas.ActualWidth
    Dim height As Double = m_inkCanvas.ActualHeight
    Dim bmpCopied As Windows.Media.Imaging.RenderTargetBitmap =
        New Windows.Media.Imaging.RenderTargetBitmap(CInt(Math.Round(width)), CInt(Math.Round(height)), 96, 96, Windows.Media.PixelFormats.[Default])
    Dim dv As Windows.Media.DrawingVisual = New Windows.Media.DrawingVisual()

    Using dc As Windows.Media.DrawingContext = dv.RenderOpen()
        Dim vb As Windows.Media.VisualBrush = New Windows.Media.VisualBrush(m_inkCanvas)
        dc.DrawRectangle(vb, Nothing, New Windows.Rect(New System.Windows.Point(), New System.Windows.Size(width, height)))
    End Using

    bmpCopied.Render(dv)
    Dim bitmap As System.Drawing.Bitmap

    Using outStream As MemoryStream = New MemoryStream()
        Dim enc As Windows.Media.Imaging.BitmapEncoder = New Windows.Media.Imaging.BmpBitmapEncoder()
        enc.Frames.Add(Windows.Media.Imaging.BitmapFrame.Create(bmpCopied))
        enc.Save(outStream)
        bitmap = New System.Drawing.Bitmap(outStream)
    End Using

    Dim qualityParam As EncoderParameter = New EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 85L)
    Dim jpegCodec As ImageCodecInfo = GetEncoderInfo("image/jpeg")
    If jpegCodec Is Nothing Then
        Return False
    End If
    Dim encoderParams As EncoderParameters = New EncoderParameters(1)
    encoderParams.Param(0) = qualityParam
    Dim btm As Bitmap = New Bitmap(bitmap)
    bitmap.Dispose()
    btm.Save(targetPath, jpegCodec, encoderParams)
    btm.Dispose()
    Return True
End Function

But this function save by inkcanvas size. How to save image by using min left and max right of strokes.

Before save

After Save