Exclude a post format from the main query in WordPRess

exc_format_query.php

<?php 
/**
 * Add a taxonomy query to pre_get_posts to remove Quote post formats from the main query
 *
 * @author Pat Ramsey
 * @link http://slash25.com
 *
 * @param array tax_query $args
 * @return modified $query
 */

function exclude_post_format( $query ) {
  // conditionals to affect only the main query on the blog page ( Settings -> Reading )
  if ( $query->is_home() && $query->is_main_query() ) {
    // tax_query takes a double array
    $args = array ( array (
	  'taxonomy' => 'post_format',
	  'field' => 'slug',
	  'terms' => 'post-format-quote',
	  'operator' => 'NOT IN'
    ));
    $query->set( 'tax_query', $args );
  }
}
add_action( 'pre_get_posts', 'exclude_post_format' );