On 11/28/2016 3:53 AM, scott wrote:
>>> Also it would be surprising to me if the
>>> human visual range came out exactly as a cylinder (after a brief glance
>>> of the maths involved), are you sure about this?
>>>
>>
>> The human visual range has a very irregular shape.
>>
>> https://en.wikipedia.org/wiki/File:Cie_Chart_with_sRGB_gamut_by_spigget.png
>>
>>
>> There's a lot of blank empty space around it in every color space. (The
>> one in the picture is called CIExyY I think.
>>
>> I would like to learn how to plot this irregular shape in the near
>> future.
>
> You just need the XYZ colour-matching functions in terms of wavelength.
> Look here (just click the first "Submit" to get a basic table):
>
> http://cvrl.ioo.ucl.ac.uk/cmfs.htm
>
> This table then gives you the exact XYZ values for each pure wavelength.
> XYZ is a linear representation of absolute colour, so you can do a lot
> of math with them (eg adding, averaging, mixing etc).
>
> To get the graph you linked to, you just need to calculate x and y for
> each of those wavelengths.
>
> x = X/(X+Y+Z)
> y = Y/(X+Y+Z)
>
> You'll then find that the x,y pairs give the outline of the graph you
> linked to, which are the pure wavelengths. The internal area is formed
> by mixing pure wavelengths, so roughly speaking the further you are away
> from the boundary the more "wideband" the light is.
>

Well, I don't understand that. Clipka did most of the work for me last 
time...

Maybe you could take a look at the code on the LCH image's page on 
Wikimedia and make some suggestions.

Mike

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