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Stephen <mca### [at] aol com> wrote:
> On 3/12/2017 1:22 PM, Mike Horvath wrote:
> > On 3/12/2017 9:00 AM, Stephen wrote:
> >> On 3/12/2017 12:42 PM, Mike Horvath wrote:
> >>> On Wikipedia it says, "In color spaces which include all, or most
> >>> spectral colors, they form a part of boundary of the set of all real
> >>> colors. If luminance is counted, then spectral colors form a surface,
> >>> otherwise their locus is a curve in a two-dimensional chromaticity
> >>> space."
> >>>
> >>> Is it acceptable to use the term "locus" to refer to a surface as well
> >>> as a curve? Or is does "locus" only refer to curves?
> >>>
> >>
> >> It is to me. ;)
> >> From this definition: a curve or other figure formed by all the points
> >> satisfying a particular equation of the relation between coordinates, or
> >> by a point, line, or surface moving according to mathematically defined
> >> conditions.
> >>
> >> A sphere fits that description. All points equidistant from the centre.
> >>
> >
> >
> > Okay thanks.
> >
>
>
> But remember that I have to take my socks off to count past 10. :)
>
>
> --
>
> Regards
> Stephen
:-D !
I thought POVers used only binary ?
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On 3/13/2017 10:17 AM, Mr wrote:
> Stephen <mca### [at] aolcom> wrote:
>>>
>>
>>
>> But remember that I have to take my socks off to count past 10. :)
>>
>>
>> --
>>
>> Regards
>> Stephen
>
> :-D !
> I thought POVers used only binary ?
>
I thought it pretentious to say count past 30. Which is true. Which is
how I count on my fingers. I can count in binary but it doesn't do my
arthritis any good. ;)
--
Regards
Stephen
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Am 13.03.2017 um 11:17 schrieb Mr:
>> But remember that I have to take my socks off to count past 10. :)
>
> :-D !
> I thought POVers used only binary ?
Why, no, of course they don't. POV-Ray only deals in floating-point
numbers, not binary integers ;)
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So, I want to plot this locus.
This site says it has 4400 data points.
"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."
https://rdrr.io/cran/SpecHelpers/man/CIExyz.html
I can't figure out how to download them from that site, however. Is
there another source I can get them from?
Also, I'm guessing the data set will allow me to plot a bunch of points,
which is great. But how do I create a smooth surface from those points?
Thanks!
Mike
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Translator needed:
https://en.wikipedia.org/wiki/Talk:Lab_color_space#CIELAB_images_in_article
The guy I'm talking to here is German, and I don't understand what he's
talking about. Would someone care to translate for me? Thanks.
Mike
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On 3/13/2017 3:06 PM, Mike Horvath wrote:
> So, I want to plot this locus.
>
> This site says it has 4400 data points.
>
> "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."
>
> https://rdrr.io/cran/SpecHelpers/man/CIExyz.html
>
> I can't figure out how to download them from that site, however. Is
> there another source I can get them from?
>
> Also, I'm guessing the data set will allow me to plot a bunch of points,
> which is great. But how do I create a smooth surface from those points?
>
> Thanks!
>
>
> Mike
I'm also assuming the data set will produce a 3D shape. Is that right?
Mike
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Am 13.03.2017 um 20:09 schrieb Mike Horvath:
> Translator needed:
>
> https://en.wikipedia.org/wiki/Talk:Lab_color_space#CIELAB_images_in_article
>
> The guy I'm talking to here is German, and I don't understand what he's
> talking about. Would someone care to translate for me? Thanks.
Unfortunately he's trying to write English, so I'd have to guess as well
-- even though I'm also German.
BTW, his use of the word "remission" actually seems to be closer to the
English use than to the German one:
https://en.wikipedia.org/wiki/Remission_(spectroscopy)
Whereas (according to Wikipedia) the English spectroscopy term
encompasses both diffuse /and/ specular reflection, the corresponding
German term ("Remission") seems to refer only to the diffuse component.
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Am 13.03.2017 um 20:06 schrieb Mike Horvath:
> So, I want to plot this locus.
>
> This site says it has 4400 data points.
>
> "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."
>
> https://rdrr.io/cran/SpecHelpers/man/CIExyz.html
>
> I can't figure out how to download them from that site, however.
To me this looks like the /documentation/ of some spectroscopy-related
maths package (which inevitably needs to include data tables like this one).
> Is there another source I can get them from?
You could get the CIE XYZ tristimulus data directly from the
International Commission on Illumination, aka Commission Internationale
de l'Eclairage, aka CIE, and compute xyY data from them "on the fly":
http://www.cie.co.at/
see the "Downloads" section, most notably "Selected Colorimetric Tables".
There's also the Colour & Vision Research Laboratory, which has an
extensive set of colorimetric data tables for download in various formats:
http://cvrl.ioo.ucl.ac.uk/
> Also, I'm guessing the data set will allow me to plot a bunch of points,
> which is great. But how do I create a smooth surface from those points?
Iterate over them to generate a mesh?
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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.
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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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