[How to render Drupal image field items(as responsive image!) programmatically -- PHP ] Load and render responsive image from field in Drupal 8

d8-responsive-image-programmatically.php

<?php

function _load_header_image($variables) {
  if ($node = $variables['node']) {
    // Load main_image
    $file = $node->field_main_image->entity;
    if ($file) {
      $variables = array(
        'responsive_image_style_id' => 'header_image',
        'uri' => $file->getFileUri(),
      );
      // The image.factory service will check if our image is valid.
      $image = \Drupal::service('image.factory')->get($file->getFileUri());
      if ($image->isValid()) {
        $variables['width'] = $image->getWidth();
        $variables['height'] = $image->getHeight();
      }
      else {
        $variables['width'] = $variables['height'] = NULL;
      }
      $logo_build = [
        '#theme' => 'responsive_image',
        '#width' => $variables['width'],
        '#height' => $variables['height'],
        '#responsive_image_style_id' => $variables['responsive_image_style_id'],
        '#uri' => $variables['uri'],
      ];
      // Add the file entity to the cache dependencies.
      // This will clear our cache when this entity updates.
      $renderer = \Drupal::service('renderer');
      $renderer->addCacheableDependency($logo_build, $file);

      // Return the render array as block content.
      return $logo_build;
    }
  }
  return NULL;
}

I'm just forking this to preserve it in case the original gets deleted. This code saved my bacon today!