Some Samsung monitors automatically dim the backlight when the displayed video falls below a certain brightness. For professional editing, this is a nuisance. Here’s how to prevent it, at least on the C570 series e.g. T28C570
In picture settings, find “Movie” mode. This stops the dimming. Then, you must recalibrate your monitor’s saturations, contrast, brightness, sharpness, etc., as before.
My settings, for an HDMI input from an Intel HD560 graphics chipset, are:
Also, turn off anything to do with “dynamic”, noise reduction, enhanced contrast, etc.