[R] Drawing a colour wheel - bug in hcl?

[Achim Zeileis]

On Mon, 7 Jul 2008, hadley wickham wrote:

>> If you replace this by
>>  hcl$colour <- hcl(hcl$h, hcl$c, hcl$l, fixup = FALSE)
>>
>>> with(hcl, plot(x, y, col=colour, pch=20))
>>
>> Then, the resulting "wheel" has three overlapping "holes" corresponding to
>> the colors previously fixed.
>
> Oops, thanks for pointing that out.
>
>> Also, as hue/chroma correspond to polar coordinates in the UV plane of
>> CIELUV, it makes more sense to plot wheels in the hue/chroma plane for fixed
>> luminance. To draw a hue/luminance plane for fixed chroma is harder to
>> interpret geometrically.
>
> Oooh, I guess if I'd thought about that for a couple of seconds I
> would have a realised that!  What are good values to use for luminance
> and chroma in that case?

There are some utility visualization functions in the devel-version of 
"colorspace" on R-Forge. Try:

source(url("http://r-forge.r-project.org/plugins/scmsvn/viewcvs.php/*checkout*/pkg/paper/Colorspace/visualizations.R?rev=13&root=colorspace"))
hue_chroma_plane()
chroma_luminance_plane()

> I can't seem to find a slice which gives me
> a decently wheel-like slice?  Or should I just use fixup = TRUE, or
> accept that true colour wheels displayed on rgb monitors don't look
> like wheels?

They always look a bit awkward, more like rectangles or triangles, but you 
could limit the maximum chroma, then it looks a bit more like a wheel.

hue_chroma_plane(c = 0:50)

But you can never get the full wheel if you want to balance with respect 
to luminance. Or conversely, if you construct a wheel like

hue_saturation_plane()

then it is not balanced with respect to lumincance.
Z

> Hadley
>
> -- 
> http://had.co.nz/
>
>