jsignature c# convert to png

i use below code to download jsignature to svg 64 and it works to me. but how can convert to string to png in c#?

<script src="../Scripts/jquery-3.1.1.min.js"></script>
    <script src="../libs/flashcanvas.js"></script>
    <script src="../libs/jSignature.min.js"></script>
    <script type="text/javascript">
        $(document).ready(function () {
            $("#signature").jSignature({ width: 650, height: 250 });
        });
         function GetData() {
            var $sigdiv = $("#signature");
            var datapair = $sigdiv.jSignature("getData", "svgbase64")
            var image = document.getElementById("Image1");
            image.src = "data:" + datapair[0] + "," + datapair[1]
               }
    </script>

   <div id="signature"></div>
          <input id="Button2" type="button" value="GetData" onclick="GetData()" />
        <hr />

        <asp:Image ID="Image1" runat="server" />

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