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"
							h14bByte = Integer(ctadatablock[12, 2], 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"
						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

Check out https://github.com/mbruggmann/osx-edid-overrides which is probably the best option for this currently.

@resoau Oh god, yes, that works!