A script to fix EDID problems on external monitors in Mac OS.Source:http://embdev.net/topic/284710

patch-edid.md

patch-edid.rb

A script to fix EDID problems on external monitors in Mac OS.

Additional reading

• The original forum thread
• An improved version of the script by adaugherity
• An explaination of the problem from Atomic Object's blog

Instructions

⚠️ This requires disabling SIP, so run this at your own risk. Be sure to re-enable SIP at the end.

1. Disable System Integrity Protection while in Recovery Mode. Reboot back into macOS when done.

   csrutil disable
   

2. For macOS Catalina and newer (which uses a read-only system volume), mount the system drive read/write (yes, this is in addition to disabling SIP)

   sudo mount -uw /
   

3. Connect only the problem monitor

4. Download this script in the directory containing all the display override plist files (note: even with the steps above, this command requires sudo to run):

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

   You may also want to use adaugherity's version of the script:

   cd /System/Library/Displays/Contents/Resources/Overrides
   sudo curl -O https://gist.githubusercontent.com/adaugherity/7435890/raw/patch-edid.rb
   

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

   sudo ruby patch-edid.rb
   

6. Reboot into recovery mode to re-enable SIP.

   csrutil enable
   

patch-edid.rb

#!/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