Fun with calibration part 2: chasing pretty charts and mitigating vignette
I had some free time today and went back to try to put to rest whether bt1886 gamma helps at all with these TV's. Since I had the meter out I also cleaned up my gamma2.2 20pt calibration and created a gamma 2.4 calibration.
Note: Since these TV output zero light for black, I created a target bt1886 gamma curve in HCFR which places 5% gray at gamma 2.0.
Once calibrated correctly, bt1886 gamma does help with vignette a small amount compared to gamma2.2. For a dark room the main impact of going from gamma 2.4 > 2.2 > bt1886 is reduced picture depth, with 2.4 being the best and 1886 having the least. The difference between 2.2 and bt1886 is small enough that I prefer using my 2.2 calibration as it comes out of black more smoothly and does not have artifacts in shadows that the 1886 calibration exhibits.
In a bright room, 2.2 may give better results than 2.4. The 1886 calibration does introduce some banding artifacts, likely a result of the extreme 5% adjustments in use.
Overall 2.4 is the best, assuming you can live with the resulting vignette.
I've attached a few files to this post as well. The first is the spectral sample I created for my colormunki display meter with my colormunki photo spectro. This correction file gave me a visually better calibration result than the OLED profile that came with HCFR. If you have a colormunki display or id3 meter, you can try out this correction file by downloading the attached LG OLED WRGB (65ef9500).zip and unzipping the .ccss file and put it in %USERDIR%/appdata/roaming/color
Another issue with calibrating these TV's is ASBL and ABL. ASBL (anti static image brightness limiter) detects if the image on the TV isn't changing and lowers brightness and fades to gray if so. You can see this sometimes on sports broadcast where the channel logo will fade to grayish. This has a negative impact on calibration and if you are taking a ton of reads without changing the content on the screen too much then you are going to have problems.
ABL (average brightness limiter) is simply the TV's method of limiting the overall power consumption of the TV. If you take your meter reads using too big of a pattern you will get messed up results as brighter whites will be dimmed by ABL kicking in.
The way to defeat ASBL and ABL on these TV's during calibration (with HCFR) is to download the 6 attached images and set them as a desktop wallpaper slideshow in windows, changing every minute. Then, resize your madTPG application window to be about the same size (or smaller) as the 4 boxes in the center of the screen. With the majority of the screen changing every minute and the overall brightness of the screen not exceeding the ABL limit you will get a good calibration.
I've included images from the HCFR calibration report below, if you want to see more details on the measurements (such as near black gamma) you can download HCFR
, and then download and unzip the attached bt1886 and gamma2.2 and gamma2.4 chc files.
One last note, I did some testing with dynamic contrast and found that if you really want that last bit of vignette fighting power you can try raising brightness a notch or two, and setting dynamic contrast to Low. Although increasing brightness brings black into the realm of visible light output on this TV, dynamic contrast on low seems to only crush down darker colors, while leaving the top end alone. The end result is that the TV comes out of black faster (less vignette), but for scenes where dark/black are filling the screen it can sometimes dim the screen down so that black is actually black. This seems to work especially well with the gamma2.4 calibration. YMMV and I wouldn't recommend using anything but Low for dynamic contrast as it really messes with things on the higher settings.
Gamma 2.4 calibration settings
Gamma 2.4 calibration results
Gamma 2.2 calibration settings
(better for bright room)
gamma 2.2 calibration results
bt1886 gamma calibration settings
(not recommended, introduces banding artifacts in dark shadows)
bt1886 calibration results