How to retrieve a value from an input field in a media view template

After digging through the media modal code, I came up with the answer to my question:

wp.media.controller.Custom = wp.media.controller.State.extend({

    initialize: function(){
        this.props = new Backbone.Model();
    },

    // called when the toolbar button is clicked
    customAction: function( controller ){
        // get the value of a media view template form field using
        // this.props.get('key'), where 'key' is the value of its 
        // 'data-setting' attribute
        console.log('width: ' + this.props.get('width'));
        console.log('height: ' + this.props.get('height'));
    }

});