Stiles Wiki

Module:Color contrast

This module is used primarily by

It is also used for tracking within

and for documentation in

The formulas used are stated in WCAG 2.x specifications. WCAG is the main guideline for creating accessible interfaces on the web.

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 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)
	if ( 0 <= R and R < 256 and 0 <= G and G < 256 and 0 <= B and B < 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 <= 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
		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("&#35;", "#")

	-- 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 < 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

	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 > 0) and (ratio2 > 0) and ((ratio1 + bias > ratio2) and c2 or c3) or '') .. ';'
	end

	return (ratio1 > 0) and (ratio2 > 0) and ((ratio1 + bias > 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 > 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 '', '&#[Xx]23;', '#'), '&#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 > 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

return p
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