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I have a MacBookPro11,2 connected via HDMI to a 4K television. I would like to try driving the display at various resolutions and frequencies, to see if that might alleviate some problems with signal stability. However the Displays prefpane only offers me a list of "scaled" resolutions, all of which are interpolated up to 4K, meaning the HDMI signal and monitor are still operating at 4K. Is it possible to foce the HDMI output to a specific (lower) resolution/refresh rate?

  • What resolutions does the TV support? – Allan Jun 2 '17 at 0:12
  • Sadly the vendor (Westinghouse) doesn't provide anything approaching technical specs for the display (actually made by Avision Technology Changzhou) model WD50UC4300. It claims the HDMI input supports "Up to 4K" which would suggest it can accept e.g. a 1080-line signal. – ruief Jun 2 '17 at 1:52
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    According to the specs it supports everything from 480i to 4K – Allan Jun 2 '17 at 2:39
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The answer is: Yes, this is possible.

I found a piece of trialware called SetResX that lets you set arbitrary real resolutions on the HDMI output, and it works!

I also found a video tutorial here that explains how to do that yourself with a substantial bit of effort, and without the nice UI, but I haven't tried that method.

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According to Apple, connecting your 4K TV to your HDMI port is only supported at either 3840x2160 or 4096x2160 resolutions.

You can use 4K displays and Ultra HD TVs at the following resolutions and refresh rates via the built-in HDMI port of your Mac:

  • 3840x2160 at 30 Hz refresh rate
  • 4096x2160 at 24 Hz refresh rate (mirroring is not supported at this resolution)

Per the specs of your TV, it supports 480i to 4K resolutions on HDMI. It also has PC input (VGA):

Compatible Modes

  • TV Tuner: NTSC/ATSC
  • Component: 480i, 480p, 720p, 1080i, 1080P
  • HDMI: 480i, 576i, 480P, 576P, 720P, 1080i, 1080P, 3840×2160/30Hz, 3840×2160/60Hz
  • PC: SVGA, XGA
  • Optimum Resolution: 3840x2160

If you want to get lower resolutions I recommend connecting to the VGA port on your TV (per the specs, it has a VGA port and using an HDMI to VGA adapter to drop the signal resolution.

  • The hardware in the MacBook Pro is totally capable of driving the HDMI port at lower resolutions, as long as the display supports them. The limitation is strictly in software, specifically in how they've dumbed-down the Displays prefpane from earlier versions. In any case, the answer turns out to be yes, you can use the Mac to drive the 4K display at lower resolutions. See my self-answer. – ruief Jun 3 '17 at 19:56

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