A fix is on the way.
According to a report by Forbes, Dolby has created a solution to an HDMI related Dolby Vision playback glitch that currently affects select displays, including models from LG.
The issue causes some Dolby Vision TVs to display intermittently elevated black levels when playing Dolby Vision content from external devices via HDMI. This includes DV playback from media players like the Apple TV 4K and various Ultra HD Blu-ray players -- though streaming apps integrated directly into Dolby Vision TVs do not suffer from the problem.
Thankfully, Dolby is aware of the glitch and has already developed a solution for the affected displays. Though an exact release date has not been announced yet, manufacturers will offer the fix through a future firmware update for their Dolby Vision TVs.
Dolby Vision is a proprietary end-to-end High Dynamic Range (HDR) format that covers content creation and playback through select cinemas, Ultra HD displays, and 4K titles. The process uses expanded brightness to improve contrast between dark and light aspects of an image, bringing out deeper black levels and more realistic details in specular highlights -- like the sun reflecting off of an ocean -- in specially graded Dolby Vision material. Likewise, Dolby Vision also offers a Wide Color Gamut (WCG), providing a greater range of colors than those found in traditional HD sources and TVs using the previous Rec. 709 color standard. In addition, the Dolby Vision process takes advantage of dynamic metadata, allowing it to adjust brightness levels on a scene-by-scene or even frame-by-frame basis to create a more accurate HDR experience than static metadata formats like HDR10.
Manufacturers with Dolby Vision-enabled displays include companies like LG, VIZIO, TCL, and Hisense. Likewise, Sony just released a Dolby Vision update for select TV models, but the current firmware only seems to support streaming apps and not HDMI sources. Though Sony has not announced a reason for this limitation yet, it's possible that it may have something to do with the HDMI issue detailed here.