Module:Color contrast
--
 -- This module implements
 --  {{Color contrast ratio}}
 --  {{Greater color contrast ratio}}
 --  {{ColorToLum}}
 --  {{RGBColorToLum}}
 --
 local p = {}
 local HTMLcolor = mw.loadData( 'Module:Color contrast/colors' )
 
 local function sRGB (v)
 	if (v &lt;= 0.03928) then
 		v = v / 12.92
 	else
 		v = math.pow((v+0.055)/1.055, 2.4)
 	end
 	return v
 end
 
 local function rgbdec2lum(R, G, B)
 	if ( 0 &lt;= R and R &lt; 256 and 0 &lt;= G and G &lt; 256 and 0 &lt;= B and B &lt; 256 ) then
 		return 0.2126 * sRGB(R/255) + 0.7152 * sRGB(G/255) + 0.0722 * sRGB(B/255)
 	else
 		return ''
 	end
 end
 
 local function hsl2lum(h, s, l)
 	if ( 0 &lt;= h and h &lt; 360 and 0 &lt;= s and s &lt;= 1 and 0 &lt;= l and l &lt;= 1 ) then
 		local c = (1 - math.abs(2*l - 1))*s
 		local x = c*(1 - math.abs( math.fmod(h/60, 2) - 1) )
 		local m = l - c/2
 
 		local r, g, b = m, m, m
 		if( 0 &lt;= h and h &lt; 60 ) then
 			r = r + c
 			g = g + x
 		elseif( 60 &lt;= h and h &lt; 120 ) then
 			r = r + x
 			g = g + c
 		elseif( 120 &lt;= h and h &lt; 180 ) then
 			g = g + c
 			b = b + x
 		elseif( 180 &lt;= h and h &lt; 240 ) then
 			g = g + x
 			b = b + c
 		elseif( 240 &lt;= h and h &lt; 300 ) then
 			r = r + x
 			b = b + c
 		elseif( 300 &lt;= h and h &lt; 360 ) then
 			r = r + c
 			b = b + x
 		end
 		return rgbdec2lum(255*r, 255*g, 255*b)
 	else
 		return ''
 	end
 end
 
 local function color2lum(c)
 
 	if (c == nil) then
 		return ''
 	end
 
 	-- html '#' entity
 	c = c:gsub(&quot;&amp;#35;&quot;, &quot;#&quot;)
 
 	-- whitespace
 	c = c:match( '^%s*(.-)[%s;]*$' )
 
 	-- unstrip nowiki strip markers
 	c = mw.text.unstripNoWiki(c)
 
 	-- lowercase
 	c = c:lower()
 
 	-- first try to look it up
 	local L = HTMLcolor[c]
 	if (L ~= nil) then
 		return L
 	end
 
 	-- convert from hsl
 	if mw.ustring.match(c,'^hsl%([%s]*[0-9][0-9%.]*[%s]*,[%s]*[0-9][0-9%.]*%%[%s]*,[%s]*[0-9][0-9%.]*%%[%s]*%)$') then
 		local h, s, l = mw.ustring.match(c,'^hsl%([%s]*([0-9][0-9%.]*)[%s]*,[%s]*([0-9][0-9%.]*)%%[%s]*,[%s]*([0-9][0-9%.]*)%%[%s]*%)$')
 		return hsl2lum(tonumber(h), tonumber(s)/100, tonumber(l)/100)
 	end
 
 	-- convert from rgb
 	if mw.ustring.match(c,'^rgb%([%s]*[0-9][0-9]*[%s]*,[%s]*[0-9][0-9]*[%s]*,[%s]*[0-9][0-9]*[%s]*%)$') then
 		local R, G, B = mw.ustring.match(c,'^rgb%([%s]*([0-9][0-9]*)[%s]*,[%s]*([0-9][0-9]*)[%s]*,[%s]*([0-9][0-9]*)[%s]*%)$')
 		return rgbdec2lum(tonumber(R), tonumber(G), tonumber(B))
 	end
 
 	-- convert from rgb percent
 	if mw.ustring.match(c,'^rgb%([%s]*[0-9][0-9%.]*%%[%s]*,[%s]*[0-9][0-9%.]*%%[%s]*,[%s]*[0-9][0-9%.]*%%[%s]*%)$') then
 		local R, G, B = mw.ustring.match(c,'^rgb%([%s]*([0-9][0-9%.]*)%%[%s]*,[%s]*([0-9][0-9%.]*)%%[%s]*,[%s]*([0-9][0-9%.]*)%%[%s]*%)$')
 		return rgbdec2lum(255*tonumber(R)/100, 255*tonumber(G)/100, 255*tonumber(B)/100)
 	end
 
 	-- remove leading # (if there is one) and whitespace
 	c = mw.ustring.match(c, '^[%s#]*([a-f0-9]*)[%s]*$')
 
 	-- split into rgb
 	local cs = mw.text.split(c or '', '')
 	if( #cs == 6 ) then
 		local R = 16*tonumber('0x' .. cs[1]) + tonumber('0x' .. cs[2])
 		local G = 16*tonumber('0x' .. cs[3]) + tonumber('0x' .. cs[4])
 		local B = 16*tonumber('0x' .. cs[5]) + tonumber('0x' .. cs[6])
 
 		return rgbdec2lum(R, G, B)
 	elseif ( #cs == 3 ) then
 		local R = 16*tonumber('0x' .. cs[1]) + tonumber('0x' .. cs[1])
 		local G = 16*tonumber('0x' .. cs[2]) + tonumber('0x' .. cs[2])
 		local B = 16*tonumber('0x' .. cs[3]) + tonumber('0x' .. cs[3])
 
 		return rgbdec2lum(R, G, B)
 	end
 
 	-- failure, return blank
 	return ''
 end
 
 -- This exports the function for use in other modules.
 -- The colour is passed as a string.
 function p._lum(color)
 	return color2lum(color)
 end
 
 function p._greatercontrast(args)
 	local bias = tonumber(args['bias'] or '0') or 0
 	local css = (args['css'] and args['css'] ~= '') and true or false
 	local v1 = color2lum(args[1] or '')
 	local c2 = args[2] or '#FFFFFF'
 	local v2 = color2lum(c2)
 	local c3 = args[3] or '#000000'
 	local v3 = color2lum(c3)
 	local ratio1 = -1;
 	local ratio2 = -1;
 	if (type(v1) == 'number' and type(v2) == 'number') then
 		ratio1 = (v2 + 0.05)/(v1 + 0.05)
 		ratio1 = (ratio1 &lt; 1) and 1/ratio1 or ratio1
 	end
 	if (type(v1) == 'number' and type(v3) == 'number') then
 		ratio2 = (v3 + 0.05)/(v1 + 0.05)
 		ratio2 = (ratio2 &lt; 1) and 1/ratio2 or ratio2
 	end
 
 	if css then
 		local c1 = args[1] or ''
 		if mw.ustring.match(c1, '^[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]$') or
 			mw.ustring.match(c1, '^[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]$') then
 				c1 = '#' .. c1
 		end
 		if mw.ustring.match(c2, '^[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]$') or
 			mw.ustring.match(c2, '^[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]$') then
 				c2 = '#' .. c2
 		end
 		if mw.ustring.match(v3, '^[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]$') or
 			mw.ustring.match(v3, '^[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]$') then
 				c3 = '#' .. c3
 		end
 		return 'background-color:' .. c1 .. '; color:' .. ((ratio1 &gt; 0) and (ratio2 &gt; 0) and ((ratio1 + bias &gt; ratio2) and c2 or c3) or '') .. ';'
 	end
 
 	return (ratio1 &gt; 0) and (ratio2 &gt; 0) and ((ratio1 + bias &gt; ratio2) and c2 or c3) or ''
 end
 
 function p._ratio(args)
 	local v1 = color2lum(args[1])
 	local v2 = color2lum(args[2])
 	if (type(v1) == 'number' and type(v2) == 'number') then
 		-- v1 should be the brighter of the two.
 		if v2 &gt; v1 then
 			v1, v2 = v2, v1
 		end
 		return (v1 + 0.05)/(v2 + 0.05)
 	else
 		return args['error'] or '?'
 	end
 end
 
 function p._styleratio(args)
 	local style = (args[1] or ''):lower()
 	local bg, fg = 'white', 'black'
 	local lum_bg, lum_fg = 1, 0
 
 	if args[2] then
 		local lum = color2lum(args[2])
 		if lum ~= '' then bg, lum_bg = args[2], lum end
 	end
 	if args[3] then
 		local lum = color2lum(args[3])
 		if lum ~= '' then fg, lum_fg = args[3], lum end
 	end
 
 	local slist = mw.text.split(mw.ustring.gsub(mw.ustring.gsub(style or '', '&amp;#[Xx]23;', '#'), '&amp;#35;', '#'), ';')
 	for k = 1,#slist do
 		local s = slist[k]
 		local k,v = s:match( '^[%s]*([^:]-):([^:]-)[%s;]*$' )
 		k = k or ''
 		v = v or ''
 		if (k:match('^[%s]*(background)[%s]*$') or k:match('^[%s]*(background%-color)[%s]*$')) then
 			local lum = color2lum(v)
 			if( lum ~= '' ) then bg, lum_bg = v, lum end
 		elseif (k:match('^[%s]*(color)[%s]*$')) then
 			local lum = color2lum(v)
 			if( lum ~= '' ) then bg, lum_fg = v, lum end
 		end
 	end
 	if lum_bg &gt; lum_fg then
 		return (lum_bg + 0.05)/(lum_fg + 0.05)
 	else
 		return (lum_fg + 0.05)/(lum_bg + 0.05)
 	end
 end
 
 --[[
 Use {{#invoke:Color contrast|somecolor}} directly or
 {{#invoke:Color contrast}} from a wrapper template.
 
 Parameters:
 	-- |1=	— required; A color to check.
 --]]
 function p.lum(frame)
 	local color = frame.args[1] or frame:getParent().args[1]
 	return p._lum(color)
 end
 
 function p.ratio(frame)
 	local args = frame.args[1] and frame.args or frame:getParent().args
 	return p._ratio(args)
 end
 
 function p.styleratio(frame)
 	local args = frame.args[1] and frame.args or frame:getParent().args
 	return p._styleratio(args)
 end
 
 function p.greatercontrast(frame)
 	local args = frame.args[1] and frame.args or frame:getParent().args
 	return p._greatercontrast(args)
 end