xmpmeta titel and keywords from a png-image to PHP strings

Question

I need the part "title" and "keywords" as a string. I made it finaly to read XML Metadata from a PNG-image.

$xmp = new SimpleXMLElement($getxmp);

Results in a mass of data i want to convert to a $title and $keywords string.

<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 5.6...">
<photoshop:headline>
**TITLE TITLE TITLE TITLE**
</photoshop:headline>

<rdf:bag><br>
<rdf:li>**keywoard1**</rdf:li>
<br>
<rdf:li>**keywoard2**</rdf:li>

How to get these strings?

$title= ...;
$keywords= ...;

If not saved with adobe, will the struture look different? Because " <**photoshop**:headline> ".

EDIT: i saw there is a title again without "photoshop":

<dc:title><br>
<rdf:alt><br>
<rdf:li xml:lang="x-default">
**TITLE TITLE TITLE TITLE**
</rdf:li><br>
</rdf:alt><br> 
</dc:title>