I see there is another setting that can cause this issue. Have you checked that motion lighting is disabled? You can find this under menu > picture > advanced setttings > motion lighting.
I've gone from one end of the manual to the other trying to figure this out. The TV has a function that auto dims the screen to suit the surrounding brightness of the room.. My problem is that I have all eco settings of this sort turned off.. so it's off while i'm watching TV, great.. now I go into the Hub where you can view pictures on a USB stick.. as soon as I look at the pictures, the screen dims as though motion lighting is turned on, but it's off! Anyone know how to completely turn off the display dimming while viewing pictures?
Lastly, my old Smaller size flat screen I would put the pics on my SD card on the TV and they would show as full screen top to bottom.. with my new Samsung TV, they show true resolution, which means I see them as really small in the center of the Tv.. how do I get them to show full screen?