$re = '/^(https?:\/\/(?:[^\/]+\/){9})(.*)$/m';
$str = 'https://www.example.com/img/public/vendor1/us/en/product-assets/vendor/product/green/device_230x400_a.gif';
$subst = "$1image/$2";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php