[Typo3] extension get values from fce-fields

[Henry Wilhelm]

Hi, all,
at first i have a FCE with two fields and i would like to get the values 
of both fields with a php-script, not with typoscript.
So i made a simple extension and included it in the setup of the page:

includeLibs.kdg_popup = EXT:kdg_popup/pi1/class.tx_kdgpopup_pi1.php

class.tx_kdgpopup_pi1.php has following content:
<?php
require_once(PATH_tslib.'class.tslib_pibase.php');
class tx_kdgpopup_pi1 extends tslib_pibase {
    var $prefixId = 'tx_kdgpopup_pi1';        // Same as class name
    var $scriptRelPath = 'pi1/class.tx_kdgpopup_pi1.php';    // Path to 
this script relative to the extension dir.
    var $extKey = 'kdg_popup';    // The extension key.
    var $pi_checkCHash = TRUE;

    function main($content,$conf)    {
        $this->conf=$conf;
        $this->pi_setPiVarDefaults();
        //$this->pi_loadLL();

        // parse XML data into php array
        $this->pi_initPIflexForm();

        // get the values

        $img = $this->pi_getFFvalue($this->cObj->data['pi_flexform'], 
'field_img', 'sDEF');
        $img_zoom = 
$this->pi_getFFvalue($this->cObj->data['pi_flexform'], 'field_img_zoom', 
'sDEF');
        $strlink = 'img: $img, img_zoom: img_zoom';
        return $this->pi_wrapInBaseClass($strlink);
    }
}
?>

datastructure of FCE looks like this:
<field_img type="array">
    <tx_templavoila type="array">
        <title>Bild (Standard)</title>
        <eType>image</eType>
        <TypoScript>
        <![CDATA[
    10 = TEXT
    10.userFunc = tx_kdgpopup_pi1->main
        ]]>
        </TypoScript>
    </tx_templavoila>
    <TCEforms type="array">
    ...
    </TCEforms>
</field_img>
<field_img_zoom type="array">
    <tx_templavoila type="array">
        <title>Bild (Zoom)</title>
        <eType>image</eType>
    </tx_templavoila>
    <TCEforms type="array">
    ...
    </TCEforms>
</field_img_zoom>

But i can't get the values of the fields img and img_zoom. What's going 
wrong?

Please help:

Henry