Who I have the same questioned this solution

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@JohnnyG1985 wrote:

STB=Tv One VMS4100

TV=samsung model un50tu7000fxza

If I click OK to watch in 4K the channel changes and picture quality goes down and gets darker.

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4K resolution alone should look better than 1080, but adding HDR makes it look even more realistic if the TV is set up properly. As dexman said according to the model you posted your TV is Capable of both. When you say the picture quality goes down, what you are seeing is the TV switching to a 4K HDR source. You have to get the TV on to a 4K HDR source, then adjust the contrast, Brightness and backlight controls until the picture looks right. Many TVs have separate adjustment memories for SDR content and HDR content. Some base the HDR content on the SDR settings, which is a mistake since as you see, the picture often gets darker when watching HDR content. Also make sure your TV settings are set to wide color, or something similar for HDR viewing. You could also try switching the TVs mode to another like Sports or Normal when you watch HDR content, if you are currently using a Movie or Cinema mode.