Color depth limited on external display connected to Surface Book 2 via dock

Question

My setup:

Surface Book 2 -> Surface Dock -> Mini-displayport to full-displayport cable -> Displayport input on Dell Ultra HD 4k Monitor P2715Q

Some time in the last few weeks/months I noticed that the color depth on my external monitor had lessened.  Shadows on websites, for example, were full of harsh banding instead of smooth gradation.  This is only an issue on the external display, not the built-in one.  When investigating the display properties on the screen, it lists my monitor as "6-bit," and the Surface Book's built-in display as "8-bit."  This was definitely not the case until recently, my guess is that it's an artifact of the last firmware/Intel driver update.  (My Intel graphics driver is ver 24.20.100.6136, which appears to match the Surface Book August update.)

I'm running the external display at 4k, 60hz, 200% scaling.  In an attempt to see if the Surface Dock was to blame, I ran an HDMI cable from the monitor into an HDMI->USBC adapter (the official MS one) and into the USBC port on the Surface Book.  Lo and behold, the shadows looked correct, and the monitor was reporting correctly as 8-bit.  However, the refresh rate seemed to be capped at 30hz.  My guess is that this is because I was using an adapter, I recall reading that the only way to successfully get 4k 60hz out of this thing is via a direct displayport cable, which is what I've been using on the dock.  There's no displayport on the Surface Book 2, though, so using this adapter is my only option for testing alternatives.

My Windows version is up-to-date, this issue existed both before and after the October update.  It seems like the Firmware update was probably the dividing line.  My guess is that the color depth went back to 8-bit when skipping the dock not due to anything dock-related, but because my adapter situation limited me to 30hz.  I'm imagining some sort of bandwidth limitation where in order to hit 4k 60hz it's capping the color depth, but limiting to 30hz allows for full color depth.  I actually just tested that hypothesis, and set my monitor to only output at 30hz while connected through the dock, but that didn't restore the color depth so that might be a dead end.

As an additional data point, I've got a friend with a Surface Book 1 that I attached to my dock and configured to match mine, and the same issue exists there as well.

Is anyone else experiencing limited color depth on external displays through the dock after the August firmware/driver update?

Answer 1

Anyone have any thoughts here?

Answer 2

https://www.dell.com/community/Monitors/UP2414Q-TB-from-PC-6-bit-color/td-p/6089105

This seems to be describing my issue pretty accurately.  I first tried manually updating my intel driver to the latest one, which didn't fix the issue.  Instead I downgraded my driver to this version:

https://downloadcenter.intel.com/download/27058/Intel-Graphics-Driver-for-Windows-15-46-?product=126789

And my color depth issues are now resolved.  Now obviously this is not a great fix, I'm a year behind on driver updates, and god knows what other issues I've introduced.  So please, Microsoft, work with Intel to get this issue resolved in their latest drivers.

Answer 3

Hi Tathanen,

Thank you for reaching out. Apologies for the delayed response. To understand the issue better, let us know more details by answering the following questions:

• Were there any changes made prior to this issue aside from installing Windows Updates?

• Can you clarify if you're connecting two monitors or single monitor on your Surface Dock?

• Have you tried re-adjusting the monitor settings from default back to your customized settings?

• Do the external monitors have firmware updates as well?

To help solve this issue, we suggest that you update the Surface Dock by downloading the Surface Dock Updater. You can check this link to know more about the step by step procedure on how to use the dock updater.

Should you need additional information, you can check this article for the supported maximum refresh rate and maximum screen resolution for the Surface Book 2 when connected to an external display. To troubleshoot your Surface when connecting an external display, check it here.

Keep us updated on the outcome.

Answer 4

I didn't know there was a way to manually update dock firmware, thanks for that link.  That said, unfortunately updating the firmware did not help with the issue.  I reinstalled the newest intel drivers and the problem came back, and I installed those year-old ones and the problem again resolved.

As for your questions:

• No changes, just the normal firmware updates that came from windows update
• I'm connecting a single 4k monitor to the dock via a displayport to mini-displayport cable, no monitor beyond that
• I'm not sure what you mean for this one, but I've toggled through a variety of setting in both Windows and on the monitor itself, and none of them have helped
• I checked the monitor firmware earlier today, it's from 2015 but it's indeed the latest version

I've read plenty about what types of resolution/refresh-rate are supported with what kind of configurations, it's the reason I'm running a pure displayport cable instead of an HDMI one in the first place.  I've got 60hz 4k running just fine off the dock, since I'm only using a single external display.  Everything was fine until the intel driver updates that came with the last batch of Surface firmware updates, and everything is fine again now that I've reverted to intel drivers older than those.

Hopefully the next Surface firmware update to be released includes intel drivers that resolve this issue, but I don't have a ton of hope there, since the intel drivers included in surface firmware bundles are usually pretty old, and even the newest-as-of-today intel driver that I tried installing (this one, if it helps: https://downloadcenter.intel.com/download/28240/Intel-Graphics-Driver-for-Windows-10?product=128199) doesn't seem to include a fix for this 6-bit/8-bit mismatch as described in my original post and the dell link in my previous post.  If Microsoft's engineers could coordinate with Intel's to make sure a fix gets in for this that'd sure be great!