OT: Type on Background - Contrast Ratios

[hh]

> Jacqueline L.G. wrote:
> Does this work well enough?:
> 
> function luminanceRatio c1,c2 -- pass two RGB triplets
>    put calcLuminance(c1) into tL1
>    put calcLuminance(c2) into tL2
>    return max(tL1,tL2) / min(tL1,tL2)
> end luminanceRatio
> 
> function calcLuminance pRGB
>    -- wikipedia: Y = 0.2126 R + 0.7152 G + 0.0722 B
>    put item 1 of pRGB * 0.2126 into tR
>    put item 2 of pRGB * 0.7152 into tG
>    put item 3 of pRGB * 0.0722 into tB
>    return sum(tR,tG,tB)
>    # if sum(tR,tG,tB) > 125 then return "black"
>    # else return "white"
> end calcLuminance

In case black is also an option as color then the following
ratio, known as contrast ratio, avoids dividing by zero:

function contrastRatio c1,c2 -- pass two RGB triplets
   put calcLuminance(c1) into tL1
   put calcLuminance(c2) into tL2
   return (0.05 + max(tL1,tL2)) / (0.05 + min(tL1,tL2))
end contrastRatio