Letterbox bars affected by image brightness
I've got a Panasonic DPUB320 UHD Blu-ray player hooked up to a Sony Bravia KD-55X8509C TV via a Pioneer VSX-1131 AV receiver.
When I play a UHD disc in 2.35:1 aspect ratio, the picture is great, but the black bars at the top and bottom of the screen keep changing to various shades of grey, depending on how bright the image is. Dark scenes: black bars. Lighter scenes: grey bars. There seems to be a tipping point so that the bars will keep brightening and darkening during a scene if there's just enough light in an otherwise dark shot.
Is this a known issue? Is there a fix?
I remember having the same issue with standard Blu-rays when I first got the Bravia, but managed to find a combination of display settings on the TV that stopped it from happening. Is it the addition of HDR that might have brought the problem back?