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From: clipka
Subject: CIE xyY / D65 gamut
Date: 30 Nov 2016 03:57:31
Message: <583e4e2b@news.povray.org>
Gamut of all theoretically possible surface colours, under D65 (noon
daylight) illumination, in CIE 1931 xyY space.


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Download 'ciexyy_d65.avi.dat' (1278 KB)

From: clipka
Subject: Re: CIE xyY / A gamut
Date: 30 Nov 2016 04:10:25
Message: <583e5131@news.povray.org>
Am 30.11.2016 um 04:56 schrieb clipka:
> Gamut of all theoretically possible surface colours, under D65 (noon
> daylight) illumination, in CIE 1931 xyY space.

Ditto, but under standard illuminant A (incandescent light bulb)
illumination.


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From: clipka
Subject: Re: CIE xyY / D65 gamut
Date: 30 Nov 2016 04:23:31
Message: <583e5443@news.povray.org>
Am 30.11.2016 um 04:56 schrieb clipka:
> Gamut of all theoretically possible surface colours, under D65 (noon
> daylight) illumination, in CIE 1931 xyY space.

Illuminant F1 (daylight fluorescent - similar colour temperature, but
different spectrum) for comparison.


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Attachments:
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From: clipka
Subject: Re: CIE xyY / F4 gamut
Date: 30 Nov 2016 04:37:51
Message: <583e579f@news.povray.org>
Am 30.11.2016 um 05:09 schrieb clipka:
> Am 30.11.2016 um 04:56 schrieb clipka:
>> Gamut of all theoretically possible surface colours, under D65 (noon
>> daylight) illumination, in CIE 1931 xyY space.
> 
> Ditto, but under standard illuminant A (incandescent light bulb)
> illumination.

And now standard illuminant F4 (warm white fluorescent), which has
almost identical xy whitepoint coordinates as illuminant A, yet exhibits
a notably different gamut due to the different spectral composition
(note e.g. the obvious "flatness" of the shape near the bluish-green
horseshoe border).


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Attachments:
Download 'ciexyy_f4.avi.dat' (1140 KB)

From: clipka
Subject: Re: CIE xyY / F12 gamut
Date: 30 Nov 2016 04:49:35
Message: <583e5a5f@news.povray.org>
Am 30.11.2016 um 05:37 schrieb clipka:
> Am 30.11.2016 um 05:09 schrieb clipka:
>> Am 30.11.2016 um 04:56 schrieb clipka:
>>> Gamut of all theoretically possible surface colours, under D65 (noon
>>> daylight) illumination, in CIE 1931 xyY space.
>>
>> Ditto, but under standard illuminant A (incandescent light bulb)
>> illumination.
> 
> And now standard illuminant F4 (warm white fluorescent), which has
> almost identical xy whitepoint coordinates as illuminant A, yet exhibits
> a notably different gamut due to the different spectral composition
> (note e.g. the obvious "flatness" of the shape near the bluish-green
> horseshoe border).

And here's F12 (Philips TL83, Ultralume 30): Again similar xy whitepoint
coordinates as A and F4, yet probably the most extremely shaped gamut of
all CIE standard illuminants, due to a very pronounced emission line
spectrum.


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Attachments:
Download 'ciexyy_f12.avi.dat' (1200 KB)

From: clipka
Subject: Re: CIE xyY / E gamut
Date: 30 Nov 2016 10:46:17
Message: <583eadf9@news.povray.org>
Am 30.11.2016 um 04:56 schrieb clipka:
> Gamut of all theoretically possible surface colours, under D65 (noon
> daylight) illumination, in CIE 1931 xyY space.

And here's illuminant E (equal energy) for reference.


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Download 'ciexyy_e.avi.dat' (1267 KB)

From: Mike Horvath
Subject: Re: CIE xyY / D65 gamut
Date: 30 Nov 2016 20:03:59
Message: <583f30af$1@news.povray.org>
On 11/29/2016 10:56 PM, clipka wrote:
> Gamut of all theoretically possible surface colours, under D65 (noon
> daylight) illumination, in CIE 1931 xyY space.
>

Could you upload some of these to Wikimedia?

Mike


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From: Mike Horvath
Subject: Re: CIE xyY / D65 gamut
Date: 1 Dec 2016 21:29:08
Message: <58409624@news.povray.org>
On 11/29/2016 10:56 PM, clipka wrote:
> Gamut of all theoretically possible surface colours, under D65 (noon
> daylight) illumination, in CIE 1931 xyY space.
>

Is it possible to model the intersection between sRGB, Lab and xyY at 
the same time? I know sRGB is fully contained within the xyY 
chromaticity diagram. But want to know if it is fully contained within 
Lab, and think that visualizing them in this way might be helpful.

Mike


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From: Mike Horvath
Subject: Re: CIE xyY / D65 gamut
Date: 10 Dec 2016 23:09:13
Message: <584c8b19@news.povray.org>
On 11/29/2016 10:56 PM, clipka wrote:
> Gamut of all theoretically possible surface colours, under D65 (noon
> daylight) illumination, in CIE 1931 xyY space.
>

How did you generate the meshes?

Mike


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From: clipka
Subject: Re: CIE xyY / D65 gamut
Date: 11 Dec 2016 00:13:19
Message: <584c9a1f@news.povray.org>
Am 11.12.2016 um 00:09 schrieb Mike Horvath:
> On 11/29/2016 10:56 PM, clipka wrote:
>> Gamut of all theoretically possible surface colours, under D65 (noon
>> daylight) illumination, in CIE 1931 xyY space.
>>
> 
> How did you generate the meshes?

"It's complicated."

I struggled quite a while to come up with a reasonably elegant solution,
until at some point I realized that all maximally saturated colours for
any given brightness fall into one of the following two categories:

(A) pigments that exhibit 100% reflectivity across a single (possibly
broad) spectral band, and 0% reflectivity outside that band
(blue-green-yellow-red side of the gamut)

(B) pigments that exhibit 0% reflectivity across a single (possibly
broad) spectral band, and 100% reflectivity outside that band (purple
side of the gamut)

Additionally, it can be noted that by pretending that the range of
visible wavelengths wraps around at the red and blue ends of the
spectrum you can map category (B) to category (A), since the former can
then be interpreted as exhibiting 100% reflectivity across a single
spectral band that straddles the wraparound point.

From these principles a mesh can be computed comparatively easy by
iterating over the "position" of the corresponding spectral band in one
direction (I chose the lower-bound wavelength, but you could just as
well choose the upper-bound wavelength or the center wavelength),
somewhat corresponding to hue, and the width of the band in the other
direction, somewhat corresponding to brightness. The maximum possible
saturation will be a function of the two.

For each mesh vertex you of course still have to compute the XYZ
coordinates of the corresponding spectrum. For this you will need to
perform numerical integration of the CIE Standard Observer table data
over the corresponding range of wavelengths. (Note that this will give
you the equal-energy gamut. For a different illuminant, you need to
multiply each table entry by the illuminant's intensity at the given
wavelength.)

The mesh can be optimized by iterating over the wavelengths in
non-uniform steps, but that seems to be an art of its own, which I
didn't master to the degree I would have liked to.


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