angularjs input上传图片前获取图片的Size

app.directive("fileread", [function () {
    return {
        scope: {
            selectedFile: "=",
            changed: '&'
        },
        link: function(scope, element, attributes) {
            element.bind("change", function(changeEvent) {
                scope.$apply(function() {
                    scope.selectedFile = changeEvent.target.files[0];
                    // or all selected files:
                    // scope.fileread = changeEvent.target.files;
                    console.log('file selected.');
                    if (scope.changed()) {
                        scope.changed()(scope.selectedFile);
                    }
                });
            });
        }
    };
}]);

 $scope.showFileSelectBox = function () {
        $("#imgSelectInput").click();
    };

    $scope.imageSelected = function(file) {
                var image;
 
                if (file) {
 
                    image = new Image();
 
                    image.onload = function () {

                        $scope.editObj.Width = this.width;
                        $scope.editObj.Height = this.height;
                    };
 
                    image.src = $window.URL.createObjectURL(file);
 
                }
    };

 <button type="button"  ng-click="showFileSelectBox()">上传</button>
                            <input type="file" style="display: none" accept="image/*" fileread selectedfile="selectedImgFile" id="imgSelectInput" changed="imageSelected" />