mb_output_handler() is
ob_start() callback
function. mb_output_handler() converts
characters in the output buffer from internal character encoding to
HTTP output character encoding.
Note:
If you want to output some binary data such as image from PHP
script with PHP 4.3.0 or later, Content-Type: header must be send
using header() before any binary data was send
to client (e.g. header("Content-Type: image/png")).
If Content-Type: header was send, output character encoding
conversion will not be performed.
Note that if 'Content-Type: text/*' was send using
header(), the sending data is regarded as text,
encoding conversion will be performed using character encoding
settings.
If you want to output some binary data such as image from PHP
script with PHP 4.2.x or earlier, you must set output encoding to
"pass" using mb_http_output().