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A script to fix EDID problems on external monitors in macOS

patch-edid.rb

A script to fix EDID problems on external monitors in macOS.

Instructions

  1. Connect only the problem display.

  2. Create this directory structure (if it doesn't already exist):

    sudo mkdir -p /Library/Displays/Contents/Resources/Overrides
  3. Download this ruby script in that directory:

    cd /Library/Displays/Contents/Resources/Overrides
    sudo curl -O https://gist.githubusercontent.com/ejdyksen/8302862/raw/patch-edid.rb

    Note: You may want to use adaugherity's version of the script instead.

  4. Run the script we just downloaded (as root again). This creates a new display override plist file.

    cd /Library/Displays/Contents/Resources/Overrides
    sudo ruby patch-edid.rb
  5. Unplug and replug in the problem display.

Additional reading/acknowledgements

  • The original forum thread
  • An improved version of the script by adaugherity
  • An explaination of the problem from Atomic Object's blog
  • Thanks so much to @stackrainbow for pointing out that this can be done without disabling SIP.
  • This version appears to work in Catalina and Big Sur. See earlier revisions for what worked (with disabling SIP) in earlier versions of macOS, which require the override plist to be in a different directory.
#!/usr/bin/ruby
# Create display override file to force Mac OS X to use RGB mode for Display
# see http://embdev.net/topic/284710
#
# Update 2013-06-24: added -w0 option to prevent truncated lines
require 'base64'
data=`ioreg -l -w0 -d0 -r -c AppleDisplay`
edid_hex=data.match(/IODisplayEDID.*?<([a-z0-9]+)>/i)[1]
vendorid=data.match(/DisplayVendorID.*?([0-9]+)/i)[1].to_i
productid=data.match(/DisplayProductID.*?([0-9]+)/i)[1].to_i
puts "found display: vendorid #{vendorid}, productid #{productid}, EDID:\n#{edid_hex}"
bytes=edid_hex.scan(/../).map{|x|Integer("0x#{x}")}.flatten
puts "Setting color support to RGB 4:4:4 only"
bytes[24] &= ~(0b11000)
puts "Number of extension blocks: #{bytes[126]}"
puts "removing extension block"
bytes = bytes[0..127]
bytes[126] = 0
bytes[127] = (0x100-(bytes[0..126].reduce(:+) % 256)) % 256
puts
puts "Recalculated checksum: 0x%x" % bytes[127]
puts "new EDID:\n#{bytes.map{|b|"%02X"%b}.join}"
Dir.mkdir("DisplayVendorID-%x" % vendorid) rescue nil
f = File.open("DisplayVendorID-%x/DisplayProductID-%x" % [vendorid, productid], 'w')
f.write '<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">'
f.write "
<dict>
<key>DisplayProductName</key>
<string>Display with forced RGB mode (EDID override)</string>
<key>IODisplayEDID</key>
<data>#{Base64.encode64(bytes.pack('C*'))}</data>
<key>DisplayVendorID</key>
<integer>#{vendorid}</integer>
<key>DisplayProductID</key>
<integer>#{productid}</integer>
</dict>
</plist>"
f.close
@joevt
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joevt commented Oct 15, 2023

@apassiou What Mac, GPU, resolution, adapter, monitor? Do you mean 90° and 270° rotation? If it were 180°, then you could just turn the display upside down. 90° or 270° means the height becomes the width which is lower than the original width. So maybe the adapter doesn't like the original width. This seems like a limitation of the adapter, gpu, or the display. Did you try without the adapter?

@johntitor2049
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Hello! i'm currently using a samsung qn90b connected to a macbook m1 2020" via a dell docking station. When connected to the docking, it's running at 8bit depth while if i plug the display straight into my mac, it runs at 10bit color depth. Any workaround for this issue? thanks!!

@GetVladimir
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@johntitor2049 the dock might not have the port or the bandwidth to support 10bit color depth, or the Mac simply doesn't recognize it properly.

If possible, it would be best to connect the monitor directly when 10bit color depth is required

@Fedosov83
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How can I activate HDR support with this patch?

@GetVladimir
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@Fedosov83 I'm not sure if you can use both HDR and RGB Color Output over a typical HDMI connection. You might need USB-C to DisplayPort for that, but it might again revert to YCbCr when using that combination

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