POV-Ray : Newsgroups : povray.advanced-users : CIE 1931 color space chromaticity diagram Server Time: 17 Jun 2019 06:56:44 GMT
 CIE 1931 color space chromaticity diagram (Message 1 to 9 of 9)
 From: Mike Horvath Subject: CIE 1931 color space chromaticity diagram Date: 26 Nov 2016 16:13:47 Message: <5839b4bb\$1@news.povray.org>
```How do you plot this horseshoe shape? Is the diagram plotted in CIE XYZ
or CIE xyY color space? How do you tell if a point is inside or outside
this curve?

Mike
```
 From: Mike Horvath Subject: Re: CIE 1931 color space chromaticity diagram Date: 26 Nov 2016 16:30:45 Message: <5839b8b5\$1@news.povray.org>
```On 11/26/2016 11:13 AM, Mike Horvath wrote:
> How do you plot this horseshoe shape? Is the diagram plotted in CIE XYZ
> or CIE xyY color space? How do you tell if a point is inside or outside
> this curve?
>
> Mike
>

I found this code.

http://www.mathworks.com/matlabcentral/fileexchange/40640-computational-colour-science-using-matlab-2e/content/cieplot.m?requestedDomain=www.mathworks.com

However, there is only x and y, so it ignores the third dimension.

Mike
```
 From: clipka Subject: Re: CIE 1931 color space chromaticity diagram Date: 26 Nov 2016 16:43:40 Message: <5839bbbc\$1@news.povray.org>
```Am 26.11.2016 um 17:13 schrieb Mike Horvath:
> How do you plot this horseshoe shape? Is the diagram plotted in CIE XYZ
> or CIE xyY color space?

It can be considered a plot of CIE xyY at some arbitrary unity Y.

Alternatively, it can be considered a plot of the slice X+Y+Z=1 of the
CIE XYZ colour space projected onto the XY plane.

> How do you tell if a point is inside or outside
> this curve?

By comparing against empirically established tables. There's no way
around that.
```
 From: clipka Subject: Re: CIE 1931 color space chromaticity diagram Date: 26 Nov 2016 17:04:45 Message: <5839c0ad\$1@news.povray.org>
```Am 26.11.2016 um 17:30 schrieb Mike Horvath:
> On 11/26/2016 11:13 AM, Mike Horvath wrote:
>> How do you plot this horseshoe shape? Is the diagram plotted in CIE XYZ
>> or CIE xyY color space? How do you tell if a point is inside or outside
>> this curve?
>>
>> Mike
>>
>
> I found this code.
>
>
http://www.mathworks.com/matlabcentral/fileexchange/40640-computational-colour-science-using-matlab-2e/content/cieplot.m?requestedDomain=www.mathworks.com
>
>
> However, there is only x and y, so it ignores the third dimension.

The third dimension is Y, luminance, aka brightness.

It has a lower bound of zero, but no natural upper bound, as light can
be arbitrarily bright.
```
 From: Mike Horvath Subject: Re: CIE 1931 color space chromaticity diagram Date: 26 Nov 2016 21:31:39 Message: <5839ff3b\$1@news.povray.org>
```On 11/26/2016 12:04 PM, clipka wrote:
> Am 26.11.2016 um 17:30 schrieb Mike Horvath:
>> On 11/26/2016 11:13 AM, Mike Horvath wrote:
>>> How do you plot this horseshoe shape? Is the diagram plotted in CIE XYZ
>>> or CIE xyY color space? How do you tell if a point is inside or outside
>>> this curve?
>>>
>>> Mike
>>>
>>
>> I found this code.
>>
>>
http://www.mathworks.com/matlabcentral/fileexchange/40640-computational-colour-science-using-matlab-2e/content/cieplot.m?requestedDomain=www.mathworks.com
>>
>>
>> However, there is only x and y, so it ignores the third dimension.
>
> The third dimension is Y, luminance, aka brightness.
>
> It has a lower bound of zero, but no natural upper bound, as light can
> be arbitrarily bright.
>

Illuminant D65 seems to be quite popular. Might that not serve as an
upper bound?

Mike
```
 From: clipka Subject: Re: CIE 1931 color space chromaticity diagram Date: 26 Nov 2016 22:41:56 Message: <583a0fb4@news.povray.org>
```Am 26.11.2016 um 22:31 schrieb Mike Horvath:

>> The third dimension is Y, luminance, aka brightness.
>>
>> It has a lower bound of zero, but no natural upper bound, as light can
>> be arbitrarily bright.
>>
>
> Illuminant D65 seems to be quite popular. Might that not serve as an
> upper bound?

/Any/ illuminant can serve as an upper limit -- but the question is,
does it make sense in the context? Popularity is not a criterium here.

Unless you have a specific reason for chosing any particular whitepoint,
the only one that stands out is whitepoint E (equal energy).

Another candidate for an upper limit would be Y=1.
```
 From: Mike Horvath Subject: Re: CIE 1931 color space chromaticity diagram Date: 27 Nov 2016 01:10:10 Message: <583a3272\$1@news.povray.org>
```On 11/26/2016 5:41 PM, clipka wrote:
> Am 26.11.2016 um 22:31 schrieb Mike Horvath:
>
>>> The third dimension is Y, luminance, aka brightness.
>>>
>>> It has a lower bound of zero, but no natural upper bound, as light can
>>> be arbitrarily bright.
>>>
>>
>> Illuminant D65 seems to be quite popular. Might that not serve as an
>> upper bound?
>
> /Any/ illuminant can serve as an upper limit -- but the question is,
> does it make sense in the context? Popularity is not a criterium here.
>
> Unless you have a specific reason for chosing any particular whitepoint,
> the only one that stands out is whitepoint E (equal energy).
>
> Another candidate for an upper limit would be Y=1.
>

Well, I *think* the ColorMine formulas use D65 by default. So I will
just stick with that.

Mike
```
 From: Ive Subject: Re: CIE 1931 color space chromaticity diagram Date: 28 Nov 2016 12:02:42 Message: <583c1ce2\$1@news.povray.org>
```Am 11/26/2016 um 17:13 schrieb Mike Horvath:
> How do you plot this horseshoe shape? Is the diagram plotted in CIE XYZ
> or CIE xyY color space? How do you tell if a point is inside or outside
> this curve?
>
> Mike
>
My include file CIE.inc* contains all the necessary tables for plotting
the horseshoe diagram.

*part of my spectral render system
http://www.lilysoft.org/CGI/SR/Spectral%20Render.htm
and
Lightsys IV
http://www.ignorancia.org/en/index.php?page=Lightsys

-Ive
```
 From: Mike Horvath Subject: Re: CIE 1931 color space chromaticity diagram Date: 4 Dec 2016 16:05:02 Message: <58443eae\$1@news.povray.org>
```On 11/28/2016 7:02 AM, Ive wrote:
> Am 11/26/2016 um 17:13 schrieb Mike Horvath:
>> How do you plot this horseshoe shape? Is the diagram plotted in CIE XYZ
>> or CIE xyY color space? How do you tell if a point is inside or outside
>> this curve?
>>
>> Mike
>>
> My include file CIE.inc* contains all the necessary tables for plotting
> the horseshoe diagram.
>
> *part of my spectral render system
> http://www.lilysoft.org/CGI/SR/Spectral%20Render.htm
> and
> Lightsys IV
> http://www.ignorancia.org/en/index.php?page=Lightsys
>
> -Ive

I looked at CIE.inc briefly, and it has a lot of macros but no real
functions. I'm not sure I can adapt the code.

Mike
```