The TV does not know what is the brightest frame or what is the brightest point of the movie, so it will only be fixed in the mastering. For you to understand, for example the movie of Goodfellas(Quei bravi ragazzi) in UHD, is mastered at 4000 nits, but the brightest point of the movie is only 347 nits. If those data (maxfall) send them to the TV, as all the players do, the TV will adjust so that the image is seen as much as possible of the panel's nits as they exceed these 347 nits. In the Apple TV the TV understands that the brightest point of the whole movie, all time, is 4000 nits. So it will lower an egg the APL ("brightness" general to understand us) to be able to see some details that we are already seeing The other two failures that it has are not left behind either: it does not take anything that is not DD by passtrough and does not change resolution ( its scaled is excellent but ONLY with its iTunes movies), using as it said a simple Bilinear. In short: if you want something almost perfect, you have the Shield TV.
