Nativescript绘图板-如何获得背景图片的签名？

Question

本机脚本绘图板-如何获取带有背景图像的签名数据？

查看代码

<DrawingPad #DrawingPad1
                    height="400"    
                    id="drawingPad" 
                    penColor="#f70202" penWidth="3"  class="draw-pad"  style="background: url('~/images/deer.jpg')no-repeat center ;">
                    </DrawingPad>

角度ts代码

let pad = this.DrawingPad1.nativeElement;
  // then get the drawing (Bitmap on Android) of the DrawingPad1
  let drawingImage;
  pad.getDrawing().then(
    (data)=> {
      console.log(data);
      drawingImage = data;
      this.userImage.nativeElement.src = data;
    },(err)=> {
      console.log(err);
    }
  );

我需要获取背景数据。请建议