Remarks

This property only uses whatever the alpha channel value is for the supplied Brush. The other channels of the Brush's rendered content (Red, Green, or Blue) are ignored.

The most typical Brush for this purpose is an ImageBrush, which can be used for a variety of photo masking techniques such as a vignette. But any defined Brush (such as LinearGradientBrush) can be used. All of these brushes require a Brush object element in XAML, so this is the XAML syntax shown.

Examples

The following example creates a RadialGradientBrush with three gradient stops in the implicit GradientStopCollection. The three gradient stops specify a brush with a varying transparency, which is then applied as the OpacityMask for an Image.

<Canvas  
  xmlns="http://schemas.microsoft.com/client/2007"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"> 

  <Image Source="sampleImages/forest.jpg" Height="100">
    <Image.OpacityMask>
      <RadialGradientBrush Center="0.5,0.5">
        <!-- This gradient stop is partially transparent. -->
        <GradientStop Color="#00000000" Offset="1" />
        <!-- This gradient stop is partially transparent. -->
        <GradientStop Color="#20000000" Offset="0.8" />
        <!-- This gradient stop is fully opaque. -->
        <GradientStop Color="#FF000000" Offset="0" />
      </RadialGradientBrush>
    </Image.OpacityMask>
  </Image> 
</Canvas>

The following illustration shows the rendered result of the preceding code.

RadialGradientBrush applied to OpacityMask of an image

Applies To

Canvas, Ellipse, Glyphs, Image, InkPresenter, Line, MediaElement, Path, Polygon, Polyline, Rectangle, TextBlock

See Also

Silverlight Brushes Overview
Imaging Overview