Module:Color contrast

This module is used primarily by

{{Color contrast ratio}}

{{ColorToLum}} / {{RGBColorToLum}}

{{Color contrast conformance}}

{{Ensure AAA contrast ratio}}

{{Greater color contrast ratio}}

It is also used for tracking within

Module:Navbox

Module:Episode list

and for documentation in

Module:College color

Usage

To use this module, you may use one of the above listed templates or invoke the module directly

To compute relative luminescence

{{ColorToLum|color}} or {{#invoke:Color contrast|lum|color}}

To compute a contrast ratio between two colors

{{Color contrast ratio|color1|color2|error=?}} or {{#invoke:Color contrast|ratio|color1|color2|error=?}}

To determine which of two colors (color2a and color2b) has the greater contrast ratio with a particular color (color1)

{{Greater color contrast ratio|color1|color2a|color2b}} or {{#invoke:Color contrast|greatercontrast|color1|color2a|color2b}}

To compute the contrast ratio between the background and text colors specified in a css style string

{{#invoke:Color contrast|styleratio|css style statement string|default background color|default text color}}

---

--
-- This module implements 
--  {{Color contrast ratio}}
--  {{Greater color contrast ratio}}
--  {{ColorToLum}}
--  {{RGBColorToLum}}
--
local p = {}

local function sRGB ( v ) 
	if (v <= 0.03928) then 
		v = v / 12.92
	else
		v = math.pow((v+0.055)/1.055, 2.4)
	end
	return v
end

local function color2lum( c )

	if (c == nil) then
		return ''
	end

	local HTMLcolor = {
		white                = 1,
		silver               = 0.52711512570581,
		gray                 = 0.2158605001139,
		black                = 0,
		red                  = 0.2126,
		maroon               = 0.045891942324215,
		yellow               = 0.9278,
		olive                = 0.20027537200568,
		lime                 = 0.7152,
		green                = 0.15438342968146,
		aqua                 = 0.7874,
		teal                 = 0.16996855778968,
		blue                 = 0.0722,
		navy                 = 0.015585128108224,
		fuchsia              = 0.2848,
		purple               = 0.061477070432439,
		orange               = 0.4817026703631,

		gold                 = 0.69860877428159,
		pink                 = 0.63271070702466,
		lightpink            = 0.58566152734898,
		hotpink              = 0.34658438169715,
		deeppink             = 0.23866895828276,
		palevioletred        = 0.28754994117889,
		mediumvioletred      = 0.14371899849357,
		lightsalmon          = 0.4780675225206,
		salmon               = 0.36977241527596,
		darksalmon           = 0.40541471563381,
		lightcoral           = 0.35522120733135,
		indianred            = 0.21406134963884,
		crimson              = 0.16042199953026,
		firebrick            = 0.10724525535015,
		darkred              = 0.054889674531132,
		orangered            = 0.25516243753416,
		tomato               = 0.30638612719415,
		coral                = 0.37017930872924,
		darkorange           = 0.40016167026524,
		lightyellow          = 0.98161818392882,
		lemonchiffon         = 0.94038992245622,
		lightgoldenrodyellow = 0.93348351018297,
		papayawhip           = 0.87797100199835,
		moccasin             = 0.80083000991567,
		peachpuff            = 0.74905589878251,
		palegoldenrod        = 0.78792647887614,
		khaki                = 0.77012343394121,
		darkkhaki            = 0.45747326349994,
		cornsilk             = 0.93562110372965,
		blanchedalmond       = 0.85084439608156,
		bisque               = 0.80732327372979,
		navajowhite          = 0.76519682342785,
		wheat                = 0.74909702820482,
		burlywood            = 0.51559844533893,
		tan                  = 0.48237604163921,
		rosybrown            = 0.32319457649407,
		sandybrown           = 0.46628543696283,
		goldenrod            = 0.41919977809569,
		darkgoldenrod        = 0.27264703559993,
		peru                 = 0.30113074877936,
		chocolate            = 0.23898526114557,
		saddlebrown          = 0.097922285020521,
		sienna               = 0.13697631337098,
		brown                = 0.098224287876511,
	}
	-- whitespace
	c = c:match( '^%s*(.-)%s*$' )

	-- lowercase
	c = c:lower()

	-- first try to look it up
	local L = HTMLcolor[c]
	if (L ~= nil) then
		return L
	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 = sRGB( (16*tonumber('0x' .. cs[1]) + tonumber('0x' .. cs[2]))/255 )
		local G = sRGB( (16*tonumber('0x' .. cs[3]) + tonumber('0x' .. cs[4]))/255 )
		local B = sRGB( (16*tonumber('0x' .. cs[5]) + tonumber('0x' .. cs[6]))/255 )

		L = 0.2126 * R + 0.7152 * G + 0.0722 * B
		return L
	elseif ( #cs == 3 ) then
		local R = sRGB( (16*tonumber('0x' .. cs[1]) + tonumber('0x' .. cs[1]))/255 )
		local G = sRGB( (16*tonumber('0x' .. cs[2]) + tonumber('0x' .. cs[2]))/255 )
		local B = sRGB( (16*tonumber('0x' .. cs[3]) + tonumber('0x' .. cs[3]))/255 )

		L = 0.2126 * R + 0.7152 * G + 0.0722 * B
		return L
	end

	-- failure, return blank
	return ''
end

function p._greatercontrast(args)
	local bias = tonumber(args['bias'] or '0') or 0
	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 = 0;
	local ratio2 = 0;
	if (type(v1) == 'number' and type(v2) == 'number') then
		ratio1 = (v2 + 0.05)/(v1 + 0.05)
		ratio1 = (ratio1 < 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 < 1) and 1/ratio2 or ratio2
	end
	return (ratio1 + bias > ratio2) and c2 or c3
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 > v1 then
			v1, v2 = v2, v1
		end
		return (v1 + 0.05)/(v2 + 0.05)
	else
		return args['error'] or '?'
	end
end

function p.lum(frame)
	return color2lum(frame.args[1] or frame:getParent().args[1])
end

function p.ratio(frame)
	local args = frame.args[1] and frame.args or frame:getParent().args
	return p._ratio(args)
end

function p.greatercontrast(frame)
	local args = frame.args[1] and frame.args or frame:getParent().args
	return p._greatercontrast(args)
end

return p