Samsung support got back to me today re. light fluctation issue and said;
With regards to your query, please be informed that there is no known issue with this TV model. We can raise it to our product specialist for further investigation
So if you do have issues with the subtitles affecting the brightness on other parts of the panel, I suggest you raise this with Samsung Support. They're not reading this forum, so whatever you say here isn't being looked at.
I think they know very well that they went into a technological dead end with the QLED technology.
Their panels are fast but they're just not good to watch movies. I can see them going OLED or another road in the next iteration.
I doubt Samsung is not aware of this issue, they just don't have a solution yet. You get all kinds of funny replies from Samsung support when approached. In one case, when I showed them my video on youtube that shows this problem on the Q7FN, they replied that they don't see anything wrong in the video...
Hehe, well, they did say that maybe the brightness is encoded in the video itslef and not added by the TV. Go figure...
And yes, it happens with any content and any source, also with non HDR. Netflix + HDR is just easy to demonstrate.
I e-mailed the Italian Samsung support and they replied advising an image reset (useless of course) and mentioning a future update that should be released soon for the Q9FN model which will address "the HDR contents related issue"....but they weren't more specific than that...I don't know if they are just buying time or if this is real, but I asked for further details about ETA of the firmware update and I am still waiting...
I kind of fixed this issue on my 65” Q7FN by disabling the local dimming in the service menu. I tried some other suggested settings first, but nothing else helped. Downside is that the backlight is now fixed to a pretty low level and I already got used to the blinding brightness this tv is normally capable of. My girlfriend didn’t and she’s actually happy that the tv is dimmer now.
Anyway this is a huge improvement! Dark scenes look great as subtitles won’t cause the infamous fluctuating brightness. Praise be! I watched the original Spider-Man on SDR and it was a delight. HRD test videos from Youtube look amazing with deep colors on black background. Quickly tested one scene of Stranger Things season 2 HDR which previously looked so horrible I almost smashed the tv. Simply beautiful now! Black level looks excellent and would look good enough with a bit higher backlight level too.
As mentioned earlier, the backlight setting won’t do anything now with the local dimming disabled. It’s really odd that the setting is missing from standard menus, as that one thing changed this tv from garbage to a pretty nice one. Now I just need a way to increase the backlight level a bit… Brighter scenes would certainly look nicer then. If someone knows a setting to try in the service menu please tell. I have zero expectations that Samsung will help us and fix this in a firmware.
If someone needs detailed instructions on how to disable the local dimming and my prefered settings to make the tv look nice, just ask. I’m too lazy to write them here if nobodys interested and all the info can be found from the interweb anyway.