Very usefull

I also use a fix to theme functions.php in order to fix bad resolution problems:

/**
 * Plugin Name: FIX JETPACK PHOTON image quality (Photon Experiments)
 * Description: changing quality parameter
 * Version: 0.1.0
 */

#FIX JETPACK PHOTON image quality
#https://developer.jetpack.com/hooks/jetpack_photon_pre_args/
#https://developer.wordpress.com/docs/photon/
#https://developer.wordpress.com/docs/photon/api/#resize
#https://developer.jetpack.com/hooks/jetpack_photon_pre_args/

# PLUS: Install & just activate plugin Ultimate Photonizer in order to Photonize all content

function jeherve_custom_photon( $args ) {
    $args['quality'] = '100'; /* menos de 100 n達o funciona! plo menos no logo com o Vantage/Altair */
    $args['strip']   = 'all';
    $args['resize']   = 'null';
    
   # $args['filter']  = 'grayscale';
    return $args;
}

add_filter( 'jetpack_photon_pre_args', 'jeherve_custom_photon' );