Add custom image size.

// functions.php
add_image_size( 'sp_cover', 1980, 1200, true );
add_filter( 'image_size_names_choose', 'sp_custom_image_sizes' );
function sp_custom_image_sizes( $sizes ) {
  return array_merge( $sizes, array(
    'sp_cover' => __( 'Rosa cover' ),
  ) );
}