Re: [Phys-L] interactive 3D CIE chromaticity diagram / color vision / xy versus xyY space

[Karim Diff <karim.diff@gmail.com>]

John,

Thanks for the information about 3D diagrams. This will be very helpful
(once I become competent at using the tool of course) in my intro E&M class
where 3D visualization is often a challenge for students.

Karim Diff

On Tue, Jan 31, 2023 at 12:13 AM John Denker via Phys-l <
phys-l@mail.phys-l.org> wrote:

> Hi --
>
> You have probably seen CIE chromaticity diagrams, i.e. the standard
> horseshoe shape. It can represent any color, as perceived by the human
> eye, without regard to brightness.
>
> This xy diagram is a two-dimensional top-down projection of a three
> dimensional space, namely the CIE xyY space. It turns out there is a
> lot more going on in 3D than you could possibly discern by looking at
> the 2D plot. Some of that is to be expected, but in this case the
> amount of monkey business in the 3D plot is remarkable. In particular,
> things that are wildly nonlinear in xyY space project down onto
> straight lines in xy space.
>
> I collected some 2D diagrams ... plus a 3D diagram that you can
> rotate, interactively, which makes it easier to see the 3D
> relationships. This is nothing fancy, just something I threw together:
>
>    https://www.av8n.com/imaging/cie-xy-xyy.xhtml
>
> As an almost-separate matter, people in this group might be interested
> in the tools I used to make the interactive 3D diagram.
>
> If you are trying to understand data, from a physics experiment or
> otherwise, the first rule is to find a way to visualize the data.
> Sometimes a higher-dimensional representation is a big win. Until
> recently this has been difficult even for experts, and insanely
> difficult for non-experts, but recently the tools have been getting
> better.
>
> In particular, if you start with an .x3d file that displays a sphere,
> it's not very tricky to write a program in your favorite high-level
> language to plot a few hundred spheres ... which is how I made the xyY
> color space plots.
>
> Integrating the plot into a web page takes a little more effort, but
> compared to other approaches, this is a piece of cake. For the
> next level of detail, look here:
>    https://www.av8n.com/imaging/x3dom.xhtml
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