IPad – 4K 60hz works on iPad Pro, not on MacBook Pro

displayipadmacbook proresolution

TL;DR > I can't get 4K@60hz working on a MacBook Pro, while I can using an iPad Pro and same set up. How can I get 4K@60hz with the MacBook Pro?

Long version

I've a 12'9 inch iPad Pro (2020) and a 13 inch MacBook Pro (mid-2017, non Touch Bar, two ports on the left side only). Additionally, I've a Hub (VAVA UC-020) which supports 4K@60hz, connected to an LG 32UK550 using HDMI.

There is an information panel on the monitor menu which shows resolution and Hz. When I connect it to my iPad Pro, the resolution is 4K@60hz with even HDR working. Using the same hub, cable and port; connected to my MacBook Pro shows 4K@30hz with no option of HDR.

If I go to display settings and show all the resolutions using the option key, I can see all the low resolutions modes. Only switching to 2K low-res I can get 60hz and even HDR (but I don't care about it tbh)

I've tried all the HDMI ports, both ports on the MacBook, connecting the external power supply to to the Hub and without… and nothing worked.

Does someone have an idea of what's going on?

Best Answer

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4K Screen 60Hz Issue – Rotated vs. Standard Orientation

Your model MacBook Pro has an Intel Iris 5100 GPU that uses up to 1.5 GB of your main RAM as its graphics memory. It supports an HDMI-compatible device, including 4K, while using one Thunderbolt display, or supports two Thunderbolt displays.

In terms of external resolution, officially your Mac can display up to 2560x1600 pixels (using Thunderbolt) or up to 3840x2160 pixels at 30Hz or 4096x2160 pixels at 24Hz (using HDMI). This is why you're being limited to the choices you're getting.

MacOS – How to unlock Sierra Refresh Rate for other resolutions less than 4k

HDMI 2.0 4K60Hz might use chroma subsampling (YCbCr422 10bpc) https://www.rtings.com/tv/learn/chroma-subsampling

You can force RGB by overriding the EDID (limits you to 8bpc) https://www.mathewinkson.com/2013/03/force-rgb-mode-in-mac-os-x-to-fix-the-picture-quality-of-an-external-monitor

DisplayPort 1.2 is preferred because it has slightly more bandwidth and will allow RGB 10bpc without requiring workarounds.

2560x1440@60Hz HiDPI uses a scaled resolution of 5120x2880. This means macOS draws into a frame buffer that is 5120x2880 and the graphics card scales the frame buffer to the scaled resolutions base which is 3840x2160 in your case (SwitchResX can change the scaled resolutions base). By default, scaled resolutions are created with only one refresh rate/timing. I think the timing used for the base resolution is the last built-in timing having the same resolution as the scaled resolutions base. This is why 3840x2160 30Hz is chosen for the timing.

macOS 10.14.6 has a new hidden preference to enable multiple refresh rates for scaled resolutions (including HiDPI resolutions).

sudo defaults write /Library/Preferences/com.apple.CoreDisplay multiRefreshRateScaledModes -bool true

Each scaled resolution (and its corresponding HiDPI resolution) will then have all the timings that the scaled resolutions base has. https://www.tonymacx86.com/threads/adding-using-hidpi-custom-resolutions.133254/post-1999528

For older macOS versions, I guess you'll need code to create scaled resolutions with specific timings, and patches to CoreDisplay to allow them. Code for some (but not all) versions of macOS that might do that is in IOGraphicsLib.c at opensource.apple.com

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