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# Modul:Color contrast

```--
-- This module implements
--  {{Color contrast ratio}}
--  {{Greater color contrast ratio}}
--  {{ColorToLum}}
--  {{RGBColorToLum}}
--
local p = {}
local HTMLcolor = mw.loadData( 'Modul: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
-- 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

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._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(style or '', ';')
for k = 1,#slist do
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

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.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
```