Blured external screen when connected via USB-C docking station to Chromebook Acer Chromebook Spin 5

My external HP monitor has a certain blur when connected via HDMI through Acer USB-C Docking station. Blur is not visible on screenshot, but is visible on photograph.

Acer Chromebook Spin 514 (C514-2H-37YX) ---USB-C---> Acer USB Type C Dock D501 (G20DK2) ---HDMI---> HP ZDisplay (resolution 2560x1440)

The monitor is showing the signal is 2560x1440@60 when I check it through the monitor menu.

Display looks fine when connected directly to the Chromebook. It also works fine, when connected via dock via DisplayPort cable.

If I take screenshot, it doesn't show the blur when examined on not-blurred configuration.

I think some part of pipeline is reporting wrong resolution (even if the monitor itself is showing a native one). I think this because if I connect the screen for the first time, it stretches outside of the screen and I need to use Overscan settings of ChromeOS to correct it. However the blur is there even if I let it fully stretched. This out-of-screen picture does not happen when the screen is not blurred.

( edited the title to add the model name )

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omree

Tried to photograph the difference. You can clearly see the arrows are 3 pixels wide when blurred and Google text has stretched upper part.

Blurred:

Image: https://us.v-cdn.net/6029997/uploads/editor/ox/bmc0cl442be5.png

Not-Blurred

Image: https://us.v-cdn.net/6029997/uploads/editor/xx/4fqydzc0fshu.png

The camera was at exactly same position, but blurred image is bigger however the display size is set to small in both cases.

billsey

Spec on that dock seems to be FHD on the displays, so it's scaling your output to 1920x1080, causing the blurring...

omree

@billsey, where did you get the dock supports only FHD? The Acer USB Type C Dock D501 manual says it supports up to 3840x2160@30Hz over DP 1.2 and 3840x2160@60Hz over DP 1.4. Unfortunately the Chromebook manual only says it supports DisplayPort over USB-C, but not which version.
Because the problem doesn't happen if I connect the LCD via DisplayPort on the dock, and also because the LCD itself shows 2560x1440@60 even when it is blurry, this proofs the Dock supports the resolution. The question is why it is blurry when connected over HDMI cable (with LCD showing full native resolution).

Here is the screenshot of the Dock manual showing what resolutions are supported:

Image: https://us.v-cdn.net/6029997/uploads/editor/4q/gh8i6k9nxc4r.png

omree

billsey said:

Spec on that dock seems to be FHD on the displays, so it's scaling your output to 1920x1080, causing the blurring...

That doesn't seem to be true. When I connect LCD via DisplayPort on the Dock, it works fine - not blurred and even when blurred, the LCD resolution is still the native 2560x1440@60. The problem happens only when the LCD is connected via HDMI port (I tried all HDMI cables I have here - same result). The HDMI cables work fine when I connect the LCD to a different laptop with them.

From the Dock manual (I have 1 display connected. Tried all ports. Only HDMI is affected, DisplayPort works fine):

Image: https://us.v-cdn.net/6029997/uploads/editor/bc/phxtatdfr72o.png

omree

sorry for the (almost) duplicate post - I thought my comment was deleted, so I re-posted it, but it fact it went into an approval process...

billsey

I was just working off the product page. Reading the small print it looks like the FHD spec is for running multiple monitors, not for a single monitor as you are using.