[TYPO3-english] GMENU produces artefacts

[Santiago]

Hi,

I'm using a partially transparent png and I added "format = png" and 
"transparentBackground = 1" to TS-template.

The source-image has no artefacts at all. I tried to reduce compression of the 
source-png, but that did not change anything.
After writing text into the image with GMENU, the result looks pretty ugly.

What can I do to avoid those artefacts?

kind regards

Santiago