Wordpress add responsive srcset header image to theme

<?php
// Extract header attachement ID
$data = get_theme_mod('header_image_data');
$data = is_object($data) ? get_object_vars($data) : $data;
$header_id = is_array($data) && isset($data['attachment_id']) ? $data['attachment_id'] : false;
if($header_id) :
    // Set image sources manually
    $src = wp_get_attachment_image_src( $header_id, 'thumbnail-head' )[0];
    $srcset = wp_get_attachment_image_srcset( $header_id, 'thumbnail-head' ); ?>
    <img id="masthead-bg" src="<?php echo $src ?>" srcset="<?php echo $srcset ?>" sizes="100vw" alt="">
<?php endif; ?>

add_image_size( 'thumbnail-head', 450, 300, true );   
add_image_size( 'thumbnail-head-2x', 900, 600, true );   
add_image_size( 'thumbnail-head-4x', 1800, 1200, true ); 

function fs_custom_header_setup() {
    add_theme_support( 'custom-header', apply_filters( 'fs_custom_header_args', array(
        'default-image'          => '',
        'header-text'            => false,
        'default-text-color'     => 'ffffff',
        'width'                  => 1800,
        'height'                 => 1200,
        'flex-width'             => false,
        'flex-height'            => false,
        'wp-head-callback'       => 'fs_header_style',
    ) ) );
}
add_action( 'after_setup_theme', 'fs_custom_header_setup' );

    the_header_image_tag( array(
        'width'     => "",
        'height'    => "",
    ));