On 3/13/2017 5:19 PM, clipka wrote:
> Am 13.03.2017 um 20:12 schrieb Mike Horvath:
>
>>> "This data set gives wavelengths every 1.0 nm, along with the associated
>>> CIE xyz values for the spectral locus of the 1931 CIE chromaticity
>>> diagram. They are called xyz values here as they are called that in the
>>> original source, but they are also known as xyY or XYZ values."
> ...
>> I'm also assuming the data set will produce a 3D shape. Is that right?
>
> Not really.
>
> What the data set will give you (if you connect the dots) is a line in
> 2D space, namely the famous CIE "horseshoe".
>
> To get a 3D shape from that, you'll first have to identify what you
> really want to plot.
>
> For example, the entire CIExyY colour space would be just an extrusion
> of that horseshoe along the Y axis, stretching to positive infinity, as
> there is no theoretical limit on brightness (for practical purposes at
> any rate): The extruded horseshoe itself would represent the locus of
> all theoretically possible monochromatic colours (i.e. colours comprised
> of only a single wavelength of light), while the volume it encompasses
> would represent the locus of all theoretically possible polychromatic
> colours.
>
>
> On the other hand, the locus of all theoretially possible pigment
> colours as illuminated by a particular light source is a much more
> complex construct, and creating its shape requires some smart ideas, as
> the volume of that shape is effectively a projection from
> infinite-dimensional space (each dimension corresponding to the
> pigment's reflectivity at a particular wavelength) to 3-dimensional
> CIExyY space.
>
> That locus may even differ between light sources with identical CIExyY
> whitepoint coordinates, as it depends on the spectrum of the light
> source, and different spectra may still result in identical CIExyY
> coordinates (see "metamerism").
>
> This is precisely the project for which I did a series of animations a
> while ago.
>

Yeah, I saw those animations and wanted to reproduce them. I figured 
that the white point would need to play a part in them, but didn't 
realize there were so many pitfalls.


Mike

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