POV-Ray : Newsgroups : povray.binaries.animations : CIELCHuv D65 gamut sphere : Re: CIELCHuv D65 gamut sphere Server Time
20 Apr 2024 22:25:19 EDT (-0400)
  Re: CIELCHuv D65 gamut sphere  
From: Mike Horvath
Date: 25 Mar 2017 17:38:00
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.


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?


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.


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