WPFのInkCanvas作為蒙版透明筆跡不透明

本人最近利用inkcavas做一個蒙版的功能，結果發現筆跡稀釋了，經過一番查找發現：應該講inkcavas的背景設置為白色，然后透明，而不是將整個控件透明，具體代碼：

        <InkCanvas Name="inkContent" Grid.RowSpan="2"
                   UseCustomCursor="True"
                   Cursor="{Binding CurrentCursor,ElementName=winWhite,Mode=OneWay}"
                   EditingModeInverted="Ink" 
                   EditingMode="{Binding CurrentEditMode,ElementName=winWhite,Mode=OneWay}"
                   DefaultDrawingAttributes="{Binding CurrentPen,ElementName=winWhite,Mode=OneWay}"
                   Loaded="inkContent_Loaded" >
            <InkCanvas.Background>
                <SolidColorBrush Color="White" Opacity="0.01" />
            </InkCanvas.Background>
        </InkCanvas>