change the logo only on single post page

add_filter( 'theme_mod_jnews_header_logo', 'change_jnews_header_logo' );
add_filter( 'theme_mod_jnews_header_logo_retina', 'change_jnews_header_logo_retina' );



function change_jnews_header_logo( $value ) {

    if ( is_single() ) {
        $value = 'http://your-single-post-logo-url.png';
    }
    return $value;
}

function change_jnews_header_logo_retina( $value ) {

    if ( is_single() ) {
        $value = 'http://your-single-post-logo-retina-url.png';
    }
    return $value;
}