[R] hcl()

[Robin Hankin]

Professor Ripley

thanks for this.

>>

>> plot(1:50,pch=16,col=hcl(h=240, c=50, l=1:50))
>>
>> I get mostly blue, but also some red, dots.  Note that h=240
>> throughout.  If 240 is blue,
>> how come there's a red dot there?  Or is it just my monitor?
>

>> hcl(h=240, c=50, l=1:50, fixup=F)
>  [1] NA        NA        NA        NA        NA        NA        NA
>  [8] NA        NA        NA        NA        NA        NA        NA
> [15] NA        NA        NA        NA        NA        NA        NA
> [22] NA        NA        NA        NA        NA        NA        NA
> [29] NA        NA        NA        NA        NA        NA        NA
> [36] NA        NA        NA        "#08628E" "#126490" "#196693" 
> "#1F6995"
> [43] "#246B97" "#286E9A" "#2D709C" "#31729F" "#3575A1" "#3877A4" 
> "#3C7AA6"
> [50] "#3F7CA9"
>
> You have mainly used invalid values: you cannot have high chroma and 
> low luminance (and there are warnings to that effect on the help 
> page).
>
> Not sure the chosen mapping of out-of-gamut specs onto the sRGB gamut 
> is particularly helpful, though.
>


Yes, this is what I was missing: with fixup taking its default value
of TRUE, out-of-range combinations are silently mapped to real RGB
values, [although the description of argument fixup in the
manpage conveys this information to me only now that I have
  your example above to look at].

  If I understand your comment, my odd-looking colours are a result of  
this mapping.

So, how best to determine the maximum chroma for a given luminance and 
hue?




--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743