[TYPO3-english] PNG files with alpha channel (PNG-24) in Backend

[Jogvan Olsen]

Can anybody tell me how I can configure TYPO3 to show png files with 
alpha channel (png-24) in the backend?

At the moment I only get a almost invisibly image in BE – In FE the 
images are displayed fine with alpha channel.

Any hint?

Thanks in advance
Jogvan