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From: Mike Horvath
Subject: CIELCHuv D65 gamut sphere
Date: 25 Mar 2017 08:19:10
Message: <58d627fe@news.povray.org>
The visible gamut under D65 illumination mapped to spherical CIELCHuv 
coordinates.


Mike


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Attachments:
Download 'visible_lchuv_d65_sph_f.webm.dat' (2073 KB)

From: clipka
Subject: Re: CIELCHuv D65 gamut sphere
Date: 25 Mar 2017 09:21:46
Message: <58d636aa@news.povray.org>
Am 25.03.2017 um 09:19 schrieb Mike Horvath:
> The visible gamut under D65 illumination mapped to spherical CIELCHuv
> coordinates.

You seem to be interpreting L as a polar coordinate, which is rather
unconventional -- and as a matter of fact doesn't make much sense, since
it causes all grey tones to collapse into the center.

The official CIE LCh colout space is cylindrical in nature, not
spherical (though the visible gamut under D65 might take on a somewhat
spherical shape).


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From: Mike Horvath
Subject: Re: CIELCHuv D65 gamut sphere
Date: 25 Mar 2017 11:21:55
Message: <58d652d3@news.povray.org>
On 3/25/2017 5:21 AM, clipka wrote:
> Am 25.03.2017 um 09:19 schrieb Mike Horvath:
>> The visible gamut under D65 illumination mapped to spherical CIELCHuv
>> coordinates.
>
> You seem to be interpreting L as a polar coordinate, which is rather
> unconventional -- and as a matter of fact doesn't make much sense, since
> it causes all grey tones to collapse into the center.
>
> The official CIE LCh colout space is cylindrical in nature, not
> spherical (though the visible gamut under D65 might take on a somewhat
> spherical shape).
>

Yes, I know. Adding a bit to the beginning of the radius creates a hole 
that keeps the gray values from collapsing.


Mike


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From: clipka
Subject: Re: CIELCHuv D65 gamut sphere
Date: 25 Mar 2017 13:46:42
Message: <58d674c2$1@news.povray.org>
Am 25.03.2017 um 12:22 schrieb Mike Horvath:
> On 3/25/2017 5:21 AM, clipka wrote:
>> Am 25.03.2017 um 09:19 schrieb Mike Horvath:
>>> The visible gamut under D65 illumination mapped to spherical CIELCHuv
>>> coordinates.
>>
>> You seem to be interpreting L as a polar coordinate, which is rather
>> unconventional -- and as a matter of fact doesn't make much sense, since
>> it causes all grey tones to collapse into the center.
>>
>> The official CIE LCh colout space is cylindrical in nature, not
>> spherical (though the visible gamut under D65 might take on a somewhat
>> spherical shape).
>>
> 
> Yes, I know. Adding a bit to the beginning of the radius creates a hole
> that keeps the gray values from collapsing.

Why use this non-canonical representation of CIE LCh/Luv in the first place?


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From: Mike Horvath
Subject: Re: CIELCHuv D65 gamut sphere
Date: 25 Mar 2017 15:08:52
Message: <58d68804@news.povray.org>
On 3/25/2017 9:46 AM, clipka wrote:
> Am 25.03.2017 um 12:22 schrieb Mike Horvath:
>> On 3/25/2017 5:21 AM, clipka wrote:
>>> Am 25.03.2017 um 09:19 schrieb Mike Horvath:
>>>> The visible gamut under D65 illumination mapped to spherical CIELCHuv
>>>> coordinates.
>>>
>>> You seem to be interpreting L as a polar coordinate, which is rather
>>> unconventional -- and as a matter of fact doesn't make much sense, since
>>> it causes all grey tones to collapse into the center.
>>>
>>> The official CIE LCh colout space is cylindrical in nature, not
>>> spherical (though the visible gamut under D65 might take on a somewhat
>>> spherical shape).
>>>
>>
>> Yes, I know. Adding a bit to the beginning of the radius creates a hole
>> that keeps the gray values from collapsing.
>
> Why use this non-canonical representation of CIE LCh/Luv in the first place?
>

Back when I was learning how to use paint programs, before I learned 
what a color solid was, I came up with a spherical representation of the 
HSL color model (see attachment). I always liked the shape, and it stuck 
with me.


Mike


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Attachments:
Download 'hsl_sphere_color_solid.fs.png' (419 KB)

Preview of image 'hsl_sphere_color_solid.fs.png'
hsl_sphere_color_solid.fs.png


 

From: clipka
Subject: Re: CIELCHuv D65 gamut sphere
Date: 25 Mar 2017 15:38:19
Message: <58d68eeb$1@news.povray.org>
Am 25.03.2017 um 16:09 schrieb Mike Horvath:
> On 3/25/2017 9:46 AM, clipka wrote:
>> Am 25.03.2017 um 12:22 schrieb Mike Horvath:
>>> On 3/25/2017 5:21 AM, clipka wrote:
>>>> Am 25.03.2017 um 09:19 schrieb Mike Horvath:
>>>>> The visible gamut under D65 illumination mapped to spherical CIELCHuv
>>>>> coordinates.
>>>>
>>>> You seem to be interpreting L as a polar coordinate, which is rather
>>>> unconventional -- and as a matter of fact doesn't make much sense,
>>>> since
>>>> it causes all grey tones to collapse into the center.
>>>>
>>>> The official CIE LCh colout space is cylindrical in nature, not
>>>> spherical (though the visible gamut under D65 might take on a somewhat
>>>> spherical shape).
>>>>
>>>
>>> Yes, I know. Adding a bit to the beginning of the radius creates a hole
>>> that keeps the gray values from collapsing.
>>
>> Why use this non-canonical representation of CIE LCh/Luv in the first
>> place?
>>
> 
> Back when I was learning how to use paint programs, before I learned
> what a color solid was, I came up with a spherical representation of the
> HSL color model (see attachment). I always liked the shape, and it stuck
> with me.

Beware that the parameterization of that color solid differs
significantly from that of your CIE LCh animation: In this HSL solid, S
is quite clearly measured radially from the vertical axis. In your CIE
LCh animation, the corresponding parameter C seems to be measured
radially from the center.


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From: Mike Horvath
Subject: Re: CIELCHuv D65 gamut sphere
Date: 25 Mar 2017 17:36:28
Message: <58d6aa9c@news.povray.org>
On 3/25/2017 11:38 AM, clipka wrote:
> In this HSL solid, S
> is quite clearly measured radially from the vertical axis.
>

Nope. It is from the center point too.


Mike


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From: clipka
Subject: Re: CIELCHuv D65 gamut sphere
Date: 25 Mar 2017 20:19:47
Message: <58d6d0e3$1@news.povray.org>
Am 25.03.2017 um 18:36 schrieb Mike Horvath:
> On 3/25/2017 11:38 AM, clipka wrote:
>> In this HSL solid, S
>> is quite clearly measured radially from the vertical axis.
>>
> 
> Nope. It is from the center point too.

Just read up on HSL, and you are right: In your spherical HSL diagram,
the distance from the center of the spehere does indeed correspond to
the parameter called "Saturation" in the HSL model.

*BUT* that "Saturation" parameter differs significantly from what I'd
consider the physical definition of saturation, where only monochromatic
light would be defined as fully saturated, while white light (at any
brightness, i.e. any shade of grey if you will) would be considered
fully unsaturated, which is what the "Chroma" parameter in the CIE LCh
model corresponds to.


If you want to get anywhere close to your HSL sphere with the CIE LCh
model, you have to represent the "Chroma" parameter as distance from the
vertical axis, otherwise you'll get a torus-ish shape instead of a
sphere-ish one. I also /think/ you'd get closer to your ideal by
sticking to the fully canonical rendering, with the "Lightness"
parameter represented as distance from the bottom plane.

At any rate, publishing a non-canonical representation of the CIE LCh
model will certainly do more to confuse people about the colour model
than to educate them.


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From: Mike Horvath
Subject: Re: CIELCHuv D65 gamut sphere
Date: 25 Mar 2017 21:38:00
Message: <58d6e338$1@news.povray.org>
On 3/25/2017 4:19 PM, clipka wrote:
> Am 25.03.2017 um 18:36 schrieb Mike Horvath:
>> On 3/25/2017 11:38 AM, clipka wrote:
>>> In this HSL solid, S
>>> is quite clearly measured radially from the vertical axis.
>>>
>>
>> Nope. It is from the center point too.
>
> Just read up on HSL, and you are right: In your spherical HSL diagram,
> the distance from the center of the spehere does indeed correspond to
> the parameter called "Saturation" in the HSL model.
>

https://commons.wikimedia.org/wiki/File:HSLSphere.svg

Is this image easier to understand? It is missing the "donut hole" in 
the middle, however. So all the grays collapse to a point, unfortunately.


> *BUT* that "Saturation" parameter differs significantly from what I'd
> consider the physical definition of saturation, where only monochromatic
> light would be defined as fully saturated, while white light (at any
> brightness, i.e. any shade of grey if you will) would be considered
> fully unsaturated, which is what the "Chroma" parameter in the CIE LCh
> model corresponds to.
>


Do these figures show what you are talking about?

https://en.wikipedia.org/wiki/File:Hsl-hsv_saturation-lightness_slices.svg

It seems "chroma" needs to be converted to "saturation first". Not sure 
the best way to do this, as I haven't thought of it before.

>
> If you want to get anywhere close to your HSL sphere with the CIE LCh
> model, you have to represent the "Chroma" parameter as distance from the
> vertical axis, otherwise you'll get a torus-ish shape instead of a
> sphere-ish one. I also /think/ you'd get closer to your ideal by
> sticking to the fully canonical rendering, with the "Lightness"
> parameter represented as distance from the bottom plane.
>

I'm not concerned so much with the outer shape. The spherical 
parameterization is what's important to me. But "chroma" needs to be 
converted to "saturation" first, as in the above image.


> At any rate, publishing a non-canonical representation of the CIE LCh
> model will certainly do more to confuse people about the colour model
> than to educate them.
>

I labeled all the images as "original research", and nothing links to 
them except a user page.


Mike


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From: clipka
Subject: Re: CIELCHuv D65 gamut sphere
Date: 25 Mar 2017 22:14:31
Message: <58d6ebc7$1@news.povray.org>
Am 25.03.2017 um 22:38 schrieb Mike Horvath:
> On 3/25/2017 4:19 PM, clipka wrote:
>> Am 25.03.2017 um 18:36 schrieb Mike Horvath:
>>> On 3/25/2017 11:38 AM, clipka wrote:
>>>> In this HSL solid, S
>>>> is quite clearly measured radially from the vertical axis.
>>>>
>>>
>>> Nope. It is from the center point too.
>>
>> Just read up on HSL, and you are right: In your spherical HSL diagram,
>> the distance from the center of the spehere does indeed correspond to
>> the parameter called "Saturation" in the HSL model.
>>
> 
> https://commons.wikimedia.org/wiki/File:HSLSphere.svg
> 
> Is this image easier to understand? It is missing the "donut hole" in
> the middle, however. So all the grays collapse to a point, unfortunately.

No, it's the HSL model's definition of "Saturation" in general that I
find counter-intuitive, not your visual representations of the HSL
colour solids.


> I labeled all the images as "original research", and nothing links to
> them except a user page.

Fair enough.


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