patch-edid-mod.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'

def replacebytes (edid, pos, thebytes, newlen)
	bytepos = pos * 2
	thelen = thebytes.length
	if newlen.to_s. != ''
		thelen = newlen * 2
	end
	edid = edid[0, bytepos] + thebytes + edid[(bytepos + thelen)..-1]
	return edid
end

def repairchecksums (edid)
	blockoffset = 0
	bytes = edid.scan(/../).map{|x|Integer("0x#{x}")}.flatten
	while blockoffset * 2 < edid.length do
		checksum = (0x100-(bytes[blockoffset,126].reduce(:+) % 256)) % 256
		edid = replacebytes(edid, blockoffset + 127, sprintf("%02x", checksum), "")
		blockoffset += 128
	end
	return edid
end

def deleteblock (edid, blockoffset)
	if  blockoffset * 2 < edid.length
		edid = replacebytes(edid, blockoffset, "", 128)
		edid = replacebytes(edid, 126, sprintf("%02x", Integer(edid[252,2], 16) - 1), "")
	else
		puts "Block at #{blockoffset} doesn't exist"
	end
	return edid
end

def deleteblocktype (edid, blocktype)
	blockoffset = 128
	while blockoffset * 2 < edid.length do
		blocktag=Integer(edid[blockoffset*2, 2], 16)
		if blocktag == blocktype
			edid = deleteblock(edid, blockoffset)
		else
			blockoffset += 128
		end
	end
end

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
edid = disp["edid_hex"]
edidversion = Float(Integer(edid[0x12 * 2, 2], 16).to_s + "." + Integer(edid[0x13 * 2, 2], 16).to_s) # 1.3 or 1.4
isdigital = Integer(edid[0x14 * 2, 1], 16) > 7 # 0 or 1
puts "edid #{edidversion}"
puts "Is Digital #{isdigital}"

featuresupportbyte = Integer(edid[0x18 * 2, 2], 16)
featuresupport = (featuresupportbyte >> 3) & 3

puts "Featuresupport #{featuresupport}"

if edidversion < 1.4
	case featuresupport
	when 0
		puts "    Monochrome or Grayscale"
	when 1
		puts "    RGB color"
	when 2
		puts "    Non-RGB color"
	when 3
		puts "    Undefined"
	end
else
	case (isdigital ? "1" : "0") + featuresupport.to_s
	when "00"
		puts "    Monochrome or Grayscale"
	when "01"
		puts "    RGB color"
	when "02"
		puts "    Non-RGB color"
	when "03"
		puts "    Undefined"
	when "10"
		puts "    RGB 4:4:4"
	when "11"
		puts "    RGB 4:4:4 + YCrCb 4:4:4"
	when "12"
		puts "    RGB 4:4:4 + YCrCb 4:2:2"
	when "13"
		puts "    RGB 4:4:4 + YCrCb 4:4:4 + YCrCb 4:2:2"
	end
	newfeaturesupportbyte = (featuresupportbyte & ~0x18) | (0 << 3)
	edid = replacebytes(edid, 0x18, sprintf("%02x", newfeaturesupportbyte), "")
	puts '        changed to "Monochrome or Grayscale"'
end

blockoffset = 128
while blockoffset * 2 < edid.length do
	theblock = edid[blockoffset * 2, 254]
	blocktag = Integer(theblock[0, 2], 16)
	if blocktag == 2
		ctaversion = Integer(theblock[2, 2], 16)
		if ctaversion > 01
			puts "cta-861 extension block with new version #{ctaversion} at #{blockoffset}"
			yCbCrSupportbyte = Integer(theblock[6, 2], 16)
			yCbCrSupport = (yCbCrSupportbyte >> 4) & 3
			case yCbCrSupport
			when 0
				puts "    no yCbCr support"
			when 1
				puts "    yCbCr 4:2:2"
			when 2
				puts "    yCbCr 4:4:4"
			when 3
				puts "    yCbCr 4:4:4, yCbCr 4:2:2"
			end
			newyCbCrSupportbyte = (yCbCrSupportbyte & ~0x30) | (0 << 4)
			edid = replacebytes(edid, blockoffset + 0x03, sprintf("%02x", newyCbCrSupportbyte), "")
			puts '        changed to "no yCbCr support"'

			if ctaversion > 02
				detailedTimingDescriptorsOffset = Integer(theblock[4, 2], 16)
				ctadatablockoffset = 4
				while ctadatablockoffset < detailedTimingDescriptorsOffset do
					ctadatablocklength = (Integer(theblock[ctadatablockoffset * 2, 2], 16) & 0x1f) + 1
					ctadatablock = theblock[ctadatablockoffset * 2, ctadatablocklength * 2]
					ctatagcode = (Integer(ctadatablock[0, 2], 16) >> 5) & 0x1f
					if ctatagcode == 7
						ctatagcode = "e" + Integer(ctadatablock[2, 2], 16).to_s
					end
					puts "#{ctadatablockoffset}: tag:#{ctatagcode} length:#{ctadatablocklength} block:#{ctadatablock}"

					case ctatagcode
					when 3
						IEEEOUI = ctadatablock[6, 2] + ctadatablock[4, 2] + ctadatablock[2, 2]
						puts "Vendor Specific IEEEOUI:"
						case IEEEOUI
						when "000c03"
							puts " HDMI Licensing, LLC -> h14b VSDB"
							h14bChunk = ctadatablock[12, 2]
							if h14bChunk.length == 2
								h14bByte = Integer(h14bChunk, 16)
								h14b = (h14bByte >> 3) & 1
								case h14b
								when 0
									puts "    Support yCbCr 4:4:4 - No"
								when 1
									puts "    Support yCbCr 4:4:4 - Yes"
								end
								newh14bByte = (h14bByte & ~0x08) | (0 << 3) # 0: No (RGB only), 1: Yes (yCbCr 4:4:4)
								edid = replacebytes(edid, blockoffset + ctadatablockoffset + 6, sprintf("%02x", newh14bByte), "")
								puts "        changed to No"
							else
								puts "  Length 0, skipping"
							end
						when "c45dd8"
							puts " HDMI Forum -> hf-VSDB"
							hfByte = Integer(ctadatablock[14, 2], 16)
							hf = (hfByte >> 0) & 7
							case hf
							when 0
								puts "    4:2:0 10/12/16 bpc - No"
							when 1
								puts "    4:2:0 10 bpc - Yes"
							when 2
								puts "    4:2:0 12 bpc - Yes"
							when 3
								puts "    4:2:0 10/12 bpc - Yes"
							when 4
								puts "    4:2:0 16 bpc - Yes"
							when 5
								puts "    4:2:0 10/16 bpc - Yes"
							when 6
								puts "    4:2:0 12/16 bpc - Yes"
							when 7
								puts "    4:2:0 10/12/16 bpc - Yes"
							end
							newhfByte = (hfByte & ~0x07) | (0 << 0)
							edid = replacebytes(edid, blockoffset + ctadatablockoffset + 7, sprintf("%02x", newhfByte), "")
							puts "        changed to No"
						else
							echo " Unknown OUI"
						end
					when "e14"
						puts "yCbCr 4:2:0 Video Data Block"
					when "e15"
						puts "yCbCr 4:2:0 Capability Map Data Block at #{blockoffset+ctadatablockoffset} : #{ctadatablock}"
						ctadatablock = ctadatablock[0, 4] + ((ctadatablock[4..-1]).gsub! '.' '0')
						edid = replacebytes(edid, blockoffset + ctadatablockoffset, ctadatablock)
						puts "    Changed to ctadatablock"
					end
					
					ctadatablockoffset += ctadatablocklength
				end
			end
		else
			puts "cta-861 extension block with old version #{ctaversion} at #{blockoffset}"
		end
	else
		puts "Extension block at #{blockoffset}: type:#{blocktag}"
	end
	blockoffset += 128
end

edid = repairchecksums(edid)
bytes = edid.scan(/../).map{|x|Integer("0x#{x}")}.flatten
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

Minor issue: on line 208, replace echo with puts

Hi @fhoech, thank you for sharing the script. It seems to be much more thorough than other EDID patches so I hope it will actually fix my issue. However, I'm having trouble getting it to work. Would you mind taking a look?

Last 5 lines are the error, the rest is just for context. Is there anything I can change to make it work? Thanks!

38: tag:3 length:8 block:67d85dc401788003
patch-edid-mod.rb:161: warning: already initialized constant IEEEOUI
patch-edid-mod.rb:161: warning: previous definition of IEEEOUI was here
Vendor Specific IEEEOUI:
 HDMI Forum -> hf-VSDB
    4:2:0 10/12 bpc - Yes
        changed to No
46: tag:e15 length:3 block:e20f81
yCbCr 4:2:0 Capability Map Data Block at 174 : e20f81
Traceback (most recent call last):
	3: from patch-edid-mod.rb:67:in `<main>'
	2: from patch-edid-mod.rb:67:in `each'
	1: from patch-edid-mod.rb:214:in `block in <main>'
patch-edid-mod.rb:214:in `+': no implicit conversion of Enumerator into String (TypeError)

My colleague was able to help me. It's the first script that actually fixed the colors while maintaining the max resolution! Even though it forces 30Hz instead of 60Hz, it's still progress.

If anyone wants to try, the updated version is here: https://gist.github.com/aleskrejci/05c903f7b245bf9dd6f95b08a2afcaa1