Open the image gallery with Ionic/angularjs

You can use the cordova camera plugin

cordova plugin add org.apache.cordova.camera

Plugin Reference: https://github.com/apache/cordova-plugin-camera

Sample code

$scope.getPhoto = function() {

    var options = {
        quality: 50,
        destinationType: Camera.DestinationType.FILE_URI,
        sourceType: Camera.PictureSourceType.SAVEDPHOTOALBUM,
        mediaType: Camera.MediaType.ALLMEDIA,
        saveToPhotoAlbum: true

    };

    $cordovaCamera.getPicture(options).then(function(imageData) {
        console.log("img URI= " + imageData);        
        //Here you will be getting image data 
    }, function(err) {
        alert("Failed because: " + err);
        console.log('Failed because: ' + err);
    });

};

You need to just set sourceType option to Camera.PictureSourceType.SAVEDPHOTOALBUM

Guys at Ionic made this example: https://github.com/driftyco/ionic-example-cordova-camera/blob/master/plugins/org.apache.cordova.camera/doc/index.md

As a second option, you can try with the imagePicker plugin.

Example:

module.controller('ThisCtrl', function($scope, $cordovaImagePicker) {

  var options = {
   maximumImagesCount: 10,
   width: 800,
   height: 800,
   quality: 80
  };

  $cordovaImagePicker.getPictures(options)
    .then(function (results) {
      for (var i = 0; i < results.length; i++) {
        console.log('Image URI: ' + results[i]);
      }
    }, function(error) {
      // error getting photos
    });
});