How to display the trimmed value and the full value of a field in a same node
i answer myself:

inside node.tpl.php, this is rendering a trimmed version of my field

&lt;?php 
     print render(field_view_field('node', $node, 'field_myfieldname', array(
        'label'=&gt;'hidden', 
        'type' =&gt; 'text_summary_or_trimmed', 
        'settings'=&gt;array('trim_length' =&gt; 30),
    )));
?&gt;


and then i render my 'default' format field like always

&lt;?php print render($content['field_image_desc']); ?&gt;