Fix blurry fonts on some external monitors when using MacBook Pro Retina

README.md

How to fix blurry fonts on some external monitors when using MacBook Pro Retina

It seems that graphcis and fonts look rather blurry on some monitors when hooked up to a MacBook Pro (Retina). This might fix the issue for you:

1. Download patch-edid.rb from http://embdev.net/attachment/168316/patch-edid.rb

2. Execute in Terminal (without the $):

   $ ruby patch-edid.rb

3. Copy produced folder (example: DisplayVendorID-22f0) to /System/Library/Displays/Overrides (authorize if needed, if the folder exists, backup it before)

4. Reconnect the Display

5. Enjoy

genedid.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

@da1z
see https://stackoverflow.com/a/32661637/2571249:
you need to reboot your mac and press ⌘+R when booting up. Then go into Utilities > Terminal and type the following commands:

csrutil disable
reboot 

step 3 for el capitan and above /System/Library/Displays/Contents/Resources/Overrides/

eg.
sudo cp -R DisplayVendorID-5e3 /System/Library/Displays/Contents/Resources/Overrides/.

I got error too, but looks like patch needs some change

patch-edid.rb:11:in <main>': undefined method[]' for nil:NilClass (NoMethodError)

I tried this and got a bit of improvement