A gamma-related control changes how intermediate signal levels are mapped between dark and bright. It can affect the perceived weight of shadows and midtones without simply changing the pixel count. HDR uses its own transfer and mapping behaviour, so do not treat every SDR gamma recipe as an HDR adjustment.
Look at more than black and white
A picture can retain black and white endpoints yet make faces, walls and dim objects look too light or too dark. Use familiar SDR footage with varied tones. A single night scene is not enough because the production may intentionally suppress midtones or use unusual grading.
Account for the room
Bright surroundings and reflections can change how dark tones appear. Establish comfortable lighting before changing advanced controls. Television menu labels and numerical options differ, so consult the exact model’s explanation rather than assuming a value copied from another display will produce the same result.
Make restrained comparisons
Record the original setting, change one option and replay the same passage. Inspect faces, dark fabric and highlight detail together. If only one title looks unusual, source grading may be involved. A global correction that improves that title can make ordinary programmes flatter or heavier, so keep a neutral baseline available.