I have a Galaxy S4 GT-I9500 (Octa-core variation), it is running 4.4.2, rooted, stock Touchwiz.
The problem is that the screen starts to flicker almost as if it would want to turn off, when in low light conditions and auto-brightness on, it continues to flicker unless I set the brightness between +2 and +5. I can reproduce the issue without auto-brightness setting the brightness to the lowest, one notch above the lowest and there is no flickering. It is noticeable in white backgrounds and also when swiping down the notification center, that's the most noticeable instance but you can see it in the home screen and in any app.
I started noticing it when I had 4.2.2 Jelly bean (rooted), and I updated to Kitkat hoping it would be solved but it is the same, I updated through Kies and rooted, no Factory reset, I want to try that as last resort.
Funny thing I discovered is when I set Juice Defender to control my brightness it does not flicker even in -60% brightness, but when the dimming happens before the screen turns off it does flicker (and the dimming thing is controlled by the OS I think, not Juice Defender).
I wish I could put up a video but I don't have another phone to film it.
Anyone know if this is software or hardware? What can I do?
I'd like to add, that I changed the battery, disabled overlays in developers option, forced GPU rendering, tried Pimp my rom and played with all the settings, checked and unchecked every option in Display settings and it still flickered given the low brightness conditions.