在ionic 3应用程序中，是否可以在拍照时将透明的png覆盖在手机屏幕上

ionic cordova plugin add cordova-plugin-camera
npm install @ionic-native/camera

import { Camera, CameraOptions } from '@ionic-native/camera';

constructor(private camera: Camera) { }

takePhoto() {
  const options: CameraOptions = {
    quality: 100,
    destinationType: this.camera.DestinationType.DATA_URL,
    encodingType: this.camera.EncodingType.JPEG,
    mediaType: this.camera.MediaType.PICTURE
  };

  this.camera.getPicture(options).then((imageData) => {
    // 在此处处理拍照后的逻辑
  }, (err) => {
    console.log(err);
  });
}

<ion-content>
  <ion-button (click)="takePhoto()">拍照</ion-button>
  <div class="overlay"></div>
</ion-content>

.overlay {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: url(path/to/transparent.png) no-repeat center center;
  background-size: contain;
  pointer-events: none; /* 防止遮挡拍照按钮 */
}