CurrentRecord field value in View Mode

Hello,
On the Inventory Item form we have a button to view an image of the item.  In order to do this we need the itemid.  Everything works great in Edit mode but in View mode the itemid is undefined for the currentRecord.  Not sure why.  Why can't we get that value in view mode?

    function onclick_ViewImage() {
        var itmRec = currentRecord.get();
        var recid = itmRec.id;
        var rectype = itmRec.type;

        var itemid = itmRec.getValue({fieldId: 'itemid' });

... more code here
    }


Thanks,
Karen