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

require 'base64'

data=`ioreg -l -d0 -w 0 -r -c AppleDisplay`

edids=data.scan(/IODisplayEDID.*?<([a-z0-9]+)>/i).flatten
vendorids=data.scan(/DisplayVendorID.*?([0-9]+)/i).flatten
productids=data.scan(/DisplayProductID.*?([0-9]+)/i).flatten

displays = []
edids.each_with_index do |edid, i|
    disp = { "edid_hex"=>edid, "vendorid"=>vendorids[i].to_i, "productid"=>productids[i].to_i }
    displays.push(disp)
end

# Process all displays
if displays.length > 1
    puts "Found %d displays!  You should only install the override file for the one which" % displays.length
    puts "is giving you problems.","\n"
end
displays.each do |disp|
# Retrieve monitor model from EDID data
monitor_name=[disp["edid_hex"].match(/000000fc00(.*?)0a/){|m|m[1]}.to_s].pack("H*")
if monitor_name.empty?
    monitor_name = "Display"
end

puts "found display '#{monitor_name}': vendorid #{disp["vendorid"]}, productid #{disp["productid"]}, EDID:\n#{disp["edid_hex"]}"

bytes=disp["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" % disp["vendorid"]) rescue nil
f = File.open("DisplayVendorID-%x/DisplayProductID-%x" % [disp["vendorid"], disp["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>#{monitor_name} - forced RGB mode (EDID override)</string>
  <key>IODisplayEDID</key>
  <data>#{Base64.encode64(bytes.pack('C*'))}</data>
  <key>DisplayVendorID</key>
  <integer>#{disp["vendorid"]}</integer>
  <key>DisplayProductID</key>
  <integer>#{disp["productid"]}</integer>
</dict>
</plist>"
f.close
puts "\n"
end		# displays.each

How to use it copied from here

Thanks a bunch for the guide! Saved me from needlessly returning my MacBook, the HDMI Adapter, or my TV.

I have a few recommendations to speed up the process, which saves one boot to recovery and you never have to actually disable the System Integrity Protection (SIP), thus never really leaving the system potentially vulnerable.

1.) Start by running the .rb script.

It only generates a couple of files in your user’s directory and does not require any special rights to read the current monitor / tv configuration. (TV must be connected).

2.) Boot to into the recovery system (Cmd+R during boot).

All your files are accessible here and you have write permissions to the “Overrides” folder. Your system disk is just not mounted to / but to /Volumes/ (e.g. “/Volumes/Macintosh HD/”)

3.) Open a terminal and copy the DisplayVendor-directory. Remember that every path is now prefixed by “/Volumes/Macintosh HD/”.

E.g. I had the Ruby script in a folder “EDID-Fix” on my desktop.
-bash-3.2# cp -r /Volumes/Macintosh\ HD/Users/marcus/Desktop/EDID-Fix/DisplayVendorID-* /Volumes/Macintosh\ HD/System/Library/Displays/Contents/Resources/Overrides/

4.) Reboot to your system

Hope you find that useful.

Cheers,
Marcus