Thanks Zerosquare - Wow, that's very interesting - testing was done on a 60 hz CRT, will test now the image processing abilities on LCD-TV.

Thanks Razoola - will give MAME debugger a try.
BTW: How did you have reached this awesome 720p video quality in Youtube with your NeoGeo-Land demos? I would like to upload a video but it does look not like the original video before uploading it to Youtube.
My current way is:
- to use the -aviwrite parameter to export an unfiltered 320x224 pix .avi-video out of MAME
- upscale the video to 720x480 MP4 > it looks like original at this point
- upload the video to Youtube > their video converter messes up the image quality (max 480p) ...

Here is how it looks now: