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I'm using a spectre x360 14 with a 38" monitor lg-38WK95C-W which is supposed to have a color depth of 10bit.

When I connect my laptop with USB-C to the monitor, the default setting appears to be (reading from the advanced settings of display settings) :

  • 3840*1600

  • 60 hz

  • 6-bit color depth

Which results in very bad gradients. They all appear with ugly lines.

Now if I change the refresh rate to 30hz, the system automatically switch to 10-bits. But with 30hz it's unusable.

If I go to 'advanced display settings/display adapter/list all modes' all the modes are 32 bit (so 8 bit per channel). None offer the possibility to use 6-bit. The selected one is

'3840 by 1600, True color (32 bit), 60 Hertz'

I tried my wide laptop which is a lower end/older one, and it can display 10-bit without issue.

Any idea why windows is forcing 6-bit?

Also HDR cannot be enabled in 60Hz.

PS: My thunderbolt connector was having connectivity instability and HP had me add a regedit key as follow :

Computer\HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Class{4d36e968-e325-11ce-bfc1-08002be10318}

Add key :

RMEnablePhyRepeate REG_DWORD 0x00000000 (0)

Thanks

PaddleStroke
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  • Have you tried all USB-C ports on the laptop? Also, check the graphics driver control panel, it may have special non-standard settings and/or diagnostics on the DisplayPort connection. – Daniel B Nov 25 '21 at 16:35

1 Answers1

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After spending afternoon with HP service center and not finding the issue, sdomoeone on reddit found the issue.

There was a setting in the bios called "enable high definition USB-C DP mode"

HP service center : 0 Reddit user : 1

PaddleStroke
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