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19 Oct 2021 17:33:24 EDT (-0400)
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From: Bald Eagle
Subject: rgb stuff that will hurt your brain
Date: 25 Jun 2021 20:55:00
Message: <web.60d67ab02a16a7571f9dae3025979125@news.povray.org>
Technology connections.

https://www.youtube.com/watch?v=uYbdx4I7STg

https://www.youtube.com/watch?v=wh4aWZRtTwU

Very well done.  Some surprising results and conclusions.

It really put into perspective how color is hue, saturation, brightness,
_context_ and _physiology_.

Highly recommended.  :)


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From: BayashiPascal
Subject: Re: rgb stuff that will hurt your brain
Date: 26 Jun 2021 06:05:00
Message: <web.60d6fb83a7968526a3e088d5e0f8c582@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:
> Technology connections.
>
> https://www.youtube.com/watch?v=uYbdx4I7STg
>
> https://www.youtube.com/watch?v=wh4aWZRtTwU
>
> Very well done.  Some surprising results and conclusions.
>
> It really put into perspective how color is hue, saturation, brightness,
> _context_ and _physiology_.
>
> Highly recommended.  :)

Thank you for sharing. Very useful videos indeed.

Pascal


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From: Cousin Ricky
Subject: Re: rgb stuff that will hurt your brain
Date: 26 Jun 2021 16:42:21
Message: <60d7912d@news.povray.org>
On 2021-06-25 8:54 PM (-4), Bald Eagle wrote:
> 
> https://www.youtube.com/watch?v=uYbdx4I7STg

I noticed these problems early on when trying to render sea water.  For
reflective surfaces, RGB is usually adequate, but with absorbing media,
a primary color bias quickly becomes apparent.  It would be quite a
coincidence for deep ocean water to be *exactly* the same color as the
blue phosphor, and experiments with other colored transparent materials
confirmed my suspicions.

Enter spectral rendering.  Ive created a spectral rendering rig using
pure SDL, and clipka did an experimental patch for native POV-Ray
spectral rendering, although AFAIK he did not release that patch.

But I also started on a spectral materials module a few years ago that I
put off after running into some snags.  My idea was to create spectral
curves that resemble those of real-world materials, so as to reduce the
problems of metamerism that turn up under the 3-color model--or at least
make the quirks shown in this video reproducible with spectral
rendering.  I didn't see that clipka's patch would give the user this
level of control over spectral curves.

One problem the video did not touch on is out-of-gamut colors.  This is
especially a problem with greens and bluish greens.  We just don't
notice this much because natural greens in the real world tend to be on
the yellowish side and are far from color-saturated.  But if you look at
RGB renditions of, say, swatches of Pantone coated colors, you'll notice
that the bright greens look washed out compared to other hues.  And if
you look at their sRGB specs, you'll see that the red channel is zero!
Those pale looking greens are as bright as sRGB will allow!

While spectral rendering would not be able to display such greens in a
color system that cannot accommodate them, Ive's Yellow Magic thread and
my own experiments with my unfinished module show that spectral
rendering can actually give a brighter impression of those greens--and
of other colors as well--when rendered in context.  Compare the caustics
and dispersion of gemcuts.jpg (RGB render) with gemcuts-sr-q2.jpg
(rendered with Ive's rig).

> https://www.youtube.com/watch?v=wh4aWZRtTwU

I learned this as a child.  I used to paint a lot, and had always been
confused over where brown fit into the red-yellow-blue or CMY
subtractive system.  The mystery was resolved when I started reading
literature from Liquitex at age 13.

Essentially, brown is no different from other dark hues; we're only
confused by it because the English language happens to have a common
name for it.


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From: Mike Horvath
Subject: Re: rgb stuff that will hurt your brain
Date: 26 Jun 2021 23:12:41
Message: <60d7eca9$1@news.povray.org>
On 6/26/2021 4:42 PM, Cousin Ricky wrote:
> Essentially, brown is no different from other dark hues; we're only
> confused by it because the English language happens to have a common
> name for it.
> 

Yeah, brown confused me until I actually started messing around with 
color pickers in software. There was no education about colors for me in 
school. More like, "Here is paint. _You_ figure it out."


Mike


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From: clipka
Subject: Re: rgb stuff that will hurt your brain
Date: 26 Jun 2021 23:57:48
Message: <60d7f73c@news.povray.org>
Am 27.06.2021 um 05:12 schrieb Mike Horvath:
> On 6/26/2021 4:42 PM, Cousin Ricky wrote:
>> Essentially, brown is no different from other dark hues; we're only
>> confused by it because the English language happens to have a common
>> name for it.
>>
> 
> Yeah, brown confused me until I actually started messing around with 
> color pickers in software. There was no education about colors for me in 
> school. More like, "Here is paint. _You_ figure it out."

I guess we all know brown is the color you get when you mix all three 
basic pigments (red, blue, yellow).

Teacher claimed the result would be a neutral grey if you did it right. 
But we all know from experience that must be a blatant lie...


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From: Cousin Ricky
Subject: Re: rgb stuff that will hurt your brain
Date: 27 Jun 2021 01:02:10
Message: <60d80652$1@news.povray.org>
On 2021-06-25 8:54 PM (-4), Bald Eagle wrote:
> 
> https://www.youtube.com/watch?v=wh4aWZRtTwU

Brown in context.  N.B. Pantone 448 C is srgb <74, 65, 42> / 255.

----------[BEGIN CODE]----------
#version 3.7;

global_settings { assumed_gamma 1 }
background { rgb 1 }
#default { finish { ambient 0 diffuse 0 emission 1 } }
camera
{ orthographic
  location <6, 4.5, -1>
  right 12.15 * x
  up 7.15 * y
}

#include "colors.inc"

#for (H, 0, 11)
  #for (L, 1, 7)
    box
    { 0.075, 0.925 translate <H, L, 0>
      #local C = CHSL2RGB (<H * 30, 1, L / 8>);
      pigment { srgbft C }
    }
  #end
#end
-----------[END CODE]-----------


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From: ingo
Subject: Re: rgb stuff that will hurt your brain
Date: 27 Jun 2021 05:10:30
Message: <XnsAD5671AD44FC8seed7@news.povray.org>
in news:60d7912d@news.povray.org Cousin Ricky wrote:

> out-of-gamut

Never looked at it, do these modern screens (oled) have a better gammut?

I worked in decorative printing (roto gravure) for years and ran the 
colourlab amongst other things. Gamut is fun. We almost never used CMYK. 
Most printing was done using op to 6 spot colours with lasure inks. Inks 
where made from 8 base colours, cold and warm red, blue, yellow and a pure 
green and black. White was a no no. Then there was a load of special 
pigments. (a nice one was 24 karat gold dust for wallpaper in Russian 
hotels)

-- 
https://ingoogni.nl


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From: clipka
Subject: Re: rgb stuff that will hurt your brain
Date: 27 Jun 2021 07:44:24
Message: <60d86498$1@news.povray.org>
Am 27.06.2021 um 11:10 schrieb ingo:
> in news:60d7912d@news.povray.org Cousin Ricky wrote:
> 
>> out-of-gamut
> 
> Never looked at it, do these modern screens (oled) have a better gammut?

They tend to, yes. To the best of my knowledge, OLEDs have 
single-wavelength primaries, and a very low blacklevel, giving the 
widest gamut you can get (with 3 primaries and additive mixing that is).

RGB backlight should be able to accomplish a similar thing, though the 
non-zero blacklevel still restricts the gamut at low total brightness.


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From: Cousin Ricky
Subject: Re: rgb stuff that will hurt your brain
Date: 11 Sep 2021 20:15:00
Message: <web.613d4573a7968526fa173ab6949c357d@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:
>
> https://www.youtube.com/watch?v=wh4aWZRtTwU

Random observation: the Cleveland Browns (American football) wear orange
uniforms.


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From: Bald Eagle
Subject: Re: rgb stuff that will hurt your brain
Date: 12 Sep 2021 14:05:00
Message: <web.613e403aa79685261f9dae3025979125@news.povray.org>
More color perception stuff that will mess with your head:


https://www.dailymail.co.uk/femail/article-9947343/Optical-illusion-makes-greyscale-picture-look-like-colours.html

I smell a macro / pigment pattern thing brewing in the future...


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