ZXing - defining scanning area

Hi everyone,
can I define scanning area in ZXing.Net.Mobile? I would like to scaned only center of screen.
I using ZXingScannerView and ZXingDefaultOverlay.

<zxing:ZXingScannerView Options="{Binding ScannerOptions}" IsScanning="{Binding IsScanning}" IsAnalyzing="{Binding IsAnalyzing}" IsEnabled="True" IsTorchOn="{Binding TorchOn, Mode=TwoWay}" Result="{Binding Result, Mode=TwoWay}" ScanResultCommand="{Binding ScanCommand}" /> <zxing:ZXingDefaultOverlay Opacity="0.9" />