View source for Module:Color contrast

--
-- This module implements 
--  {{Color contrast ratio}}
--  {{Greater 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
		return (v2 + 0.05)/(v1 + 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