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Force RGB mode in Mac OS X to fix the picture quality of an external monitor

I recently bought a MacBook Pro (with ‘Retina’ screen), but when I hooked it up to my Dell U2410 monitor via HDMI cable I was shocked by the poor picture quality. The contrast was all wrong and text was misshapen. No amount of calibration in the monitor or software would fix it.

Short answer: OS X thinks my monitor is a TV, and is using the YCbCr colour space rather than RGB. I had to override an EDID setting to force the RGB colour space, and it is now working correctly.

Long answer: I haven’t owned a Mac for a while and had forgotten how difficult much of the “Apple community” can be when it comes to anything that can’t be adjusted in System Preferences. Googling for problems with external monitors on MacBooks found dozens of threads on official and unofficial Apple forums, all full of people with the same problem. The most common response was to blame the monitor, despite assurances from the stricken users that the monitor worked beautifully in Linux and Windows, even on the same machine under Boot Camp.

“You just haven’t calibrated it!”, “You are just too used to Retina now!”, “You just need to buy a Thunderbolt display!” Apple people also like to solve problems by throwing more money at it. (I realise that owning a Mac makes me an Apple person, too. Hypocritical self-loather?)

My lucky break was reading that the current colour space was “YCbCr” when I was browsing the monitor’s settings menu. I was sure that it was using RGB when hooked up to my PC, so I started searching instead for forcing RGB mode in OS X. It didn’t appear to be available out-of-the-box, but I have had some experience in overriding EDID settings for similar purposes so I searched instead for that.

I found this thread on the forums. Mr Schwarz, thanks very much. Your thread and script was incredibly helpful and informative. It was written to fix problems connecting an external monitor via DisplayPort, but it fixed my HDMI issue just the same. I’ve summarised the required steps below.

My last word is to wonder what Apple is playing at. It seems that this problem has been reported by a lot of people for a long time, and I expect it would require a fairly simple software update. Do they just not care about those using third-party components, or are they actively attempting to force people on to Thunderbolt displays?

How to force RGB in Mac OS X

  1. Download the patch-edid.rb script from the forums thread above and put it in your home directory.
  2. Connect only the external monitor(s) in question (I closed my MacBook lid, for example). The script will make override files for any connected monitor.
  3. Type “ruby patch-edid.rb” in Terminal.
  4. A new folder will be created in your home directory. Move it into the “/System/Library/Displays/Overrides” folder. If Finder tells you that you are overwriting an existing folder, consider backing it up first.
  5. Restart your computer, enjoy your monitor.

To undo the changes, either delete the folder you had copied to the Overrides folder (if it didn’t already exist) or replace it with the folder you had backed up.


I’m not running OS X any more, but if you’re having trouble with any of these steps, please have a look through the comments below (and note that there are multiple pages). Many questions have been answered with helpful tips from others.

Update, 27 Oct 2013: If you’ve applied this fix before, the OS X Mavericks update will overwrite it. I’ve successfully re-applied the fix by following exactly the same steps, and other commenters below have done so, too.

Update, 13 Nov 2013: Andrew comments below that he has modified the script to add some useful new features, and provides a link to his GitHub for those wishing to use it instead.

Update, 28 Nov 2013: If the process appears to work but doesn’t seem to make a difference, consider Tom’s comments below. Depending on your monitor an extra tweak may be required.

Update, 26 May 2014: If you have had trouble with limited resolutions being available after the fix, check out Ibrahim’s comments here.


Kitty Bessie

I thought I would have to do this, but I didn’t. Instead I used the big fancy dual cable Mini Display Port to DVI Adaptor (purchased by my company when the MPB was bought recently and didn’t work on my 24) to connect to my Dell P2314H as it worked fine, and used my partner’s spare basic single cable Mini Display Port to DVI adaptor to connect my Dell U2413, which was the one that didn’t work originally on the bigger, fancier MDP to DVI. So now, without having to rewrite anything, I have my dual monitors up and running and looking sweet! So, if you don’t want to fiddle around for hours with the code, ask around and try a few different cables and connectors that people have lying around in their desks and cupboards. Worked for me, might work for you too! :)

Conrad Rodas

Thank you for your file. Unfortunately it didn’t work for me.

I have a MacPro (new model) with Thunderbolt to HDMI and a Dell 2711.
This setup worked with 10.9 Mavericks. I had to press “Alt” while
pressing “scaled” in preferences in order to get 2556×1440 as an option.
As soon as I upgraded to 10.10 (currently on 10.10.3 beta) the
resolution went away and the highest I can reach is 1920×1080.

I downloaded all 3 scrips, even the alternative. I put the Ruby file in
my home folder, run the script, create the new folder with the new text
file with I name DisplayProductID-a055, restart my computer and nothing.
I still only see 1920×1080 as my highest resolution possible. I am putting it
in the correct folder System<Library<Displays<Overrides

What can I be doing wrong?

Please please help!


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