LG OLED TVs Suffer from Unfixable Gamma Shift When Variable Refresh Rate Is Enabled

Image: LG

Astounding picture quality aside, LG’s 2019 and 2020 OLED TVs provide plenty of gamer-friendly HDMI 2.1 features such as ALLM (Auto Low Latency Mode) and VRR (Variable Refresh Rate). Unfortunately, HDTVTest’s Vincent Teoh has reported that the latter is marred by a significant caveat: gamma/brightness shift.

What this basically means is that when VRR is enabled on LG’s HDMI 2.1 OLED TVs, the picture diverges from the calibrated values, resulting in an incorrect increase in black levels. As the OLED Association explains in its letter (which confirms the issue), this is a notable problem that could result in a loss of shadow detail in scenes.

Forbes’ reported LGE’s 2019 and 2020 OLED TVs variable refresh rate (VRR) implementation sometimes causes the image to undergo a brightness/gamma shift that makes dark areas in games look greyer and more washed out than they do with VRR turned off. By toggling the AMD FreeSync feature in the LG OLED TVs menus on and off with the Gears 5 HDR calibration screen playing with the VRR feature on, the black floor is raised and, as a result, there’s less visible shading detail in the dark areas of the left side of the Gears 5 calibration image, which is noticeable when the TV’s instant game response feature is turned off and switched to a picture preset other than the Game. There are also reports of noticeable instability/flickering in some dark gaming image areas when using VRR on LGs 2019 OLEDs.

Gamma for OLED is optimized and fixed for 120Hz by establishing a fixed charging time for OLED sub-pixels. VRR is used when the frame rate is less than 120 Hz. When the OLED TV uses framerates less than 120Hz, the gamma curve is inconsistent with the frame rate. For example, a 40Hz frame rate is longer than 120Hz frame rate. Therefore, the lower frame rates results in sub pixels that are overcharged, causing flickering of dark gray images, which is noticeable for dark images rather than bright ones, because human eyes are more sensitive to low gray colors. LGD will likely solve this problem establishing multiple gamma curves optimized for lower frame rates.

Unfortunately for LG 2019 and 2020 OLED owners, Teoh noted that the VRR gamma shift issue is inherent to the panel, which means that it can’t be fixed via software means and will require newer hardware.

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