Signature Pad View does not contain getImage

I have use the Xamarin Control SignaturePad Form in my PCL project. The code as below:

    public class DigitalSignature : ContentPage
     {
            SignaturePadView sign = new SignaturePadView();

            public DigitalSignature()
            {
                Button btnOk = new Button
                {
                    Text = "Ok",
                    BackgroundColor = Color.FromHex("#ff6600"),
                    HorizontalOptions = LayoutOptions.End,
                    WidthRequest = 100,
                    HeightRequest = 35,
                    FontSize = 15
                };

                btnOk.Clicked += btnOk_Clicked;

                sign = new SignaturePadView()
                {
                    SignatureLineColor = Color.Red,
                    StrokeColor = Color.Black,
                    StrokeWidth = 10f,
                    HeightRequest = 150,
                    BackgroundColor = Color.White,
                    ClearText = "Clear Me"
                };
                sign.CaptionText = "pls sign here";


                Content = new StackLayout
                {
                    Children = {
                        sign,
                        btnOk
                    }
                };

            }

            private void btnOk_Clicked(object sender, EventArgs e)
            {

            }
        }

How I can get the signature as image and store in the database? In the signaturepadview do not has the getImage() function. Anyone has idea how I can do that?

Thanks,
Derick