Fix: Blurry display on HDMI-connected Dell 2415H monitor on MacBook Pro

On the MacBook Pro (2017, with Touchbar) that I currently use as my primary development computer at work, after I "docked" the computer (reconnected all external monitors and devices) this morning, my monitors were in the wrong order.

Further, the display on one of the external monitors -- a Dell 2415H, connected via USB-C port → USB-C to HDMI adapter → HDMI cable → HDMI port -- had an extremely blurry display. That monitor also now had "overscan" of about a centimeter; that is, the image extended past the viewable area of the screen in all directions (so that I could only see the bottom edge of the menu bar at the top of the screen).

Fixing the display order was a simple matter of going into System Preferences → Displays → Arrangement, and dragging the monitors back into the proper order.

However, it took a little longer to figure out a solution to the blurriness issue. In the System Preferences → Displays window for the blurry monitor, the Resolution radio button was set to "Default for display" as usual. When I changed it to Scaled, the available values were "1080i" (selected), and 720p.

Changing the setting to 720p caused the display to be sharp again, but everything on that monitor ended up being sized way too large.  (Plus, I then was only presumably getting 720 pixels of vertical resolution, instead of the 1920x1080 of which the monitor was capable.)

The solution turned out to be to close the Displays windows, unplug and replug that monitor's HDMI cable, and then open System Preferences → Displays again.  After doing that, the Displays window → Color tab → Resolution (scaled) selection for the blurry monitor now displayed two additional options which weren't there before: "1080p" and "1600 x 900".



Changing the selection to the now-available "1080p" fixed the problem: All text and images on the monitor became nice and sharp again, and the overscan went away.