Luminance Overshoot OLED CX / GX
The LG X-Series OLEDs (CX, GX) suffer from luminance overshoot.
It is some sort of dynamic lumanince overshoot at changes at very low luminance levels. Pixels seem to "overdrive" on luminance when coming out of black. Instead of transitioning from black to a dark grey, they briefly flash to a higher luminance level.
It only appears in motion for a couple of milliseconds and disappears quickly. It is highly distracting in movies and mostly games, where the camera moves a lot.
Here are some examples of the issue, both in synthetic test patterns and real life content (please watch in a dim environment):
It is not an individual problem, as many users are affected. See the corresponding thread on the AVS Forums:
Pages 497 onwards.
I have done some research on the issue and these are my findings:
- Some sets show it, othes don't. It might be that some sets show it more prominently than others.
I have asked numerous people whose judgement I trust to run the test (see 4) and their sets are definitely not affected.EDIT: More and more people found that when looking closely they can see the issue. It looks like all sets are affected, but not to the same degree.
- It happens regardless of input, picture mode and any resonable Gamma / Brightness settings (on my set I have to set brightness to 63 to not see it at all).
- It affects SDR, HDR and DV.
- There are no settings whatsoever that can mitigate the overshoot.
- Pixel Refresh does not help. Resetting the TV to factory settings does not help.
- I calibrated my set, both automatically using a 1D LUT and manually using a 22pt correction in Calman Home for LG to no avail. This issue can't be ironed out by calibration.
- The only dependence on content is that with dimly lit scenes and bad lighting it becomes more apparent. It is also there in well lit scenes on transitions to black, if you look closely. I can see it in any fade to and out of black. It is more apparent with video games, since there is more movement.
- There is an easy way to test for this issue: Download the test pattern "Grey linearization" from the following link (it's free, thanks to Mehanik), play it on the PC in windowed mode and move the player window around the desktop. You will see the overshoot in motion. It's an HDR test file, but you can play it in SDR and HDR. 01. Ramps – Google Drive
- I had my first panel replaced. My second panel shows the same problem. I immediately told the service person who installed the new panel. He acknowledged there was something wrong and took my set to their workshop for testing. It came back with the result "Everything within specifications". No further comments. I accepted with reservations, hoping one of the updates would fix the issue. They didn't.
- This issue existed before LG implemented/changed the dithering on the CX with the 03.21.16 update. I fact, it has existed since I bought the TV back in August.
What I don't know is what exactly is the root of the problem.
Maybe it is the panel, maybe it is in fact a fault in the main board, or maybe it is a software issue. The fact that some sets don't show the issue speaks against the latter. My exchange panel showing the same issue as my first one speaks against the former, so my guess at the moment is that is a main board issue and or an issue with dithering or how the pixels are addressed.
The issue is similar to the Chrominance Overshoot issue, which had plagues the 8-Series of OLEDS (C8 etc.), and which has been reported about here by Vincent Teoh (HDTVTest):
LG, please fix this issue!