Drupal 8 preprocess custom image render from node

banner_image.php

<?php
$node = \Drupal::routeMatch()->getParameter('node');

// Add a Banner to pages when a Featured Image is used
if ($node && !$node->field_featured_image->isEmpty()) {

  $image = $node->field_featured_image->entity;

  // Create the Render Array
  $variables['banner_image'] = [
    '#theme' => 'image_style',
    '#uri' => $image->uri->value,
    '#alt' => $image->alt,
    '#title' => $image->title,
    '#style_name' => 'banner_image'
  ];
}