A script to fix EDID problems on external monitors in macOS

patch-edid.md

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.

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

Look for the DisplayLink USB device in System Information.app. DisplayLink uses USB 3.0. USB 3.0 is ≈ 4 Gbps (5 Gbps times 8/10 for the 8b10b encoding = 4 Gbps).

Video data rate is pixel clock times bits per pixel. 4K60 usually has a pixel clock of 533 MHz. 533 million pixels per second x 30 bits per pixel = 15.9 billions bits per second (Gbps). The CPU must compress video to transmit to the DisplayLink video controller at reasonable refresh rates (60 Hz).

I don't think there are any faster DisplayLink devices. The CPU is doing all the work. A faster DisplayLink would require the CPU to do more work.

To lessen the work required by the CPU, reduce the resolution and/or refresh rate.

Look for the DisplayLink USB device in System Information.app. DisplayLink uses USB 3.0. USB 3.0 is ≈ 4 Gbps (5 Gbps times 8/10 for the 8b10b encoding = 4 Gbps).

Video data rate is pixel clock times bits per pixel. 4K60 usually has a pixel clock of 533 MHz. 533 million pixels per second x 30 bits per pixel = 15.9 billions bits per second (Gbps). The CPU must compress video to transmit to the DisplayLink video controller at reasonable refresh rates (60 Hz).

I don't think there are any faster DisplayLink devices. The CPU is doing all the work. A faster DisplayLink would require the CPU to do more work.

To lessen the work required by the CPU, reduce the resolution and/or refresh rate.

yes i found it it shows up to 5gbps oh well so not much we can do about that. Well thank you very much for your help at least now i know that there is no solution to this.

it is what it is.

Thank you!