I eventually did manage to find something to make it reasonably acceptable, but its still far from perfect. You need to search for a video on YouTube called "Fix Auto Dimming for Samsung TV's". It does involve delving into the hidden setup menus in the TV however, and you'll need to be carefull not to change the wrong thing. But it's basically some settings called PWM that set how dark the screen goes when it detects a mostly black scene. To access the menu on the TU7000 I think you turn off the TV, then press info, settings,mute and power on the remote. It'll reboot and you'll have the hidden menus in screen. Follow the instructions in the video. I think I set then values to 85 rather than 100, and combined with turning "Shadow detail" up to 3 in the normal TV menus it's ok now. When you've made the changes power the TV back off and on. This seems to reset most of the TV settings as well so you need to go back and turn off auto dimming etc if you'd done that before.
Hope this helps
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