Module:Color contrast

Documentation for this module may be created at Module:Color contrast/doc

--
-- 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 <= 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 )
	return 0.2126 * sRGB(R/255) + 0.7152 * sRGB(G/255) + 0.0722 * sRGB(B/255)
end

local function hsl2lum( h, s, l )
	local lum = ''
	if ( 0 <= h and h < 360 and 0 <= s and s <= 1 and 0 <= l and l <= 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 <= h and h < 60 ) then
			r = r + c
			g = g + x
		elseif( 60 <= h and h < 120 ) then
			r = r + x
			g = g + c
		elseif( 120 <= h and h < 180 ) then
			g = g + c
			b = b + x
		elseif( 180 <= h and h < 240 ) then
			g = g + x
			b = b + c
		elseif( 240 <= h and h < 300 ) then
			r = r + x
			b = b + c
		elseif( 300 <= h and h < 360 ) then
			r = r + c
			b = b + x
		end
		lum = rgbdec2lum(255*r, 255*g, 255*b)
	end
	return lum
end

local function color2lum( c )

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

   	-- 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]*%)$') then
		local h = mw.ustring.match(c,'^hsl%([%s]*([0-9][0-9]*)[%s]*,[%s]*[0-9][0-9]*%%[%s]*,[%s]*[0-9][0-9]*%%[%s]*%)$')
		local s = mw.ustring.match(c,'^hsl%([%s]*[0-9][0-9]*[%s]*,[%s]*([0-9][0-9]*)%%[%s]*,[%s]*[0-9][0-9]*%%[%s]*%)$')
		local l = mw.ustring.match(c,'^hsl%([%s]*[0-9][0-9]*[%s]*,[%s]*[0-9][0-9]*%%[%s]*,[%s]*([0-9][0-9]*)%%[%s]*%)$')
		return hsl2lum(tonumber(h), tonumber(s)/100, tonumber(l)/100)
   	end

	-- 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

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