What's wrong with plugin with ngx appended

i install imagepicker plugin and it comes with ngx appended.
and when I do ionic serve with iphone version in chrome, it has below error.
normally, it should evoke error saying cordova not available .
ngx appended is for ionic 4???
I deleted ngx on import like belows
import { ImagePicker } from ‘@ionic-native/image-picker’;
then, it evoke error
on constructor(public imagePicker:ImagePicker )
cannot find name ImagePicker

CameraselectPage.html:15 ERROR TypeError: Object(...) is not a function
    at ImagePicker.getPictures (index.js:32)
    at CameraselectPage.webpackJsonp.168.CameraselectPage.getPhoto (cameraselect.ts:69)
    at Object.eval [as handleEvent] (CameraselectPage.html:15)
    at handleEvent (core.js:13589)
    at callWithDebugContext (core.js:15098)
    at Object.debugHandleEvent [as handleEvent] (core.js:14685)
    at dispatchEvent (core.js:10004)
    at core.js:10629
    at HTMLButtonElement.<anonymous> (platform-browser.js:2628)
    at t.invokeTask (polyfills.js:3)