POV-Ray : Newsgroups : povray.binaries.images : More Rainbows pt 2 Server Time
1 Aug 2024 00:22:49 EDT (-0400)
  More Rainbows pt 2 (Message 1 to 5 of 5)  
From: Trevor G Quayle
Subject: More Rainbows pt 2
Date: 10 Feb 2009 13:55:00
Message: <web.4991cc9e3aa58f3d81c811d20@news.povray.org>
The second one is in glass (with photons, refractive only).

http://barberofcivil.deviantart.com/art/Glass-Rainbow-112450799


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From: Bob
Subject: Re: More Rainbows pt 2
Date: 10 Feb 2009 16:29:41
Message: <4991f1c5$1@news.povray.org>
No need to actually work with glass when it can be ray traced in POV. I like 
these minimilist kind of things.

Brings up a question of color that's more often than not been a frustration 
of mine. The orange looks brown... or more precisely, it looks like a tea 
drink.
Many times I tried to get a traffic cone fluorescent orange color and 
failed. Even if the color can be attained alone, any scene change (lighting, 
etc.) is almost sure to lose the bright orange color. That seems to go for 
yellow sometimes, too.
I think it's video card and LCD related, because the few times I've compared 
on another display it looks different. Doubt it would only be gamma at fault 
(besides my own fault).


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From: Cousin Ricky
Subject: Re: More Rainbows pt 2
Date: 10 Feb 2009 17:35:01
Message: <web.4991ffd7dddf939e85de7b680@news.povray.org>
"Bob" <omniverse*charter!net> wrote:
> Brings up a question of color that's more often than not been a frustration
> of mine. The orange looks brown... or more precisely, it looks like a tea
> drink.
> Many times I tried to get a traffic cone fluorescent orange color and
> failed. Even if the color can be attained alone, any scene change (lighting,
> etc.) is almost sure to lose the bright orange color. That seems to go for
> yellow sometimes, too.
> I think it's video card and LCD related, because the few times I've compared
> on another display it looks different. Doubt it would only be gamma at fault
> (besides my own fault).

I read that it has to do with the way our eyes interpret the combination of red
and green phosphors.  I can't remember where, though.  Normally I'd take care
of the problem by boosting the finish ( diffuse } value, but this won't work
with glass.


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From: clipka
Subject: Re: More Rainbows pt 2
Date: 10 Feb 2009 18:00:00
Message: <web.4992060bdddf939e797ec15b0@news.povray.org>
"Bob" <omniverse*charter!net> wrote:
> Many times I tried to get a traffic cone fluorescent orange color and
> failed.

That's no surprise, because this orange (or rather, "signal red" if it's the
stuff I'm thinking of) is "excessively" orange / red.

As the real-life pigment *is* in fact fluorescent (= absorbs ultraviolet light
and re-emits it in the visible spectrum), it will (seem to) "reflect" e.g. more
red light than a perfectly white surface would.

To simulate it in POV-Ray, you need to (1) set (some of) the color components to
values >1.0 as appropriate, and (2) reduce the overall lighting of the scene so
that your "plain white" is less bright than the display can get.

I recommend using HDR output (available in MegaPOV 1.2.1 or current POV betas,
and viewable with e.g. the freeware programs "HDRView" or "HDRShop"), because
the file format can easily represent color values >100%, so you can later toy
around with overall brightness (and gamma, for that matter).


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From: Bob
Subject: Re: More Rainbows pt 2
Date: 10 Feb 2009 18:51:50
Message: <49921316$1@news.povray.org>
"Cousin Ricky" <ric### [at] yahoocom> wrote in message 
news:web.4991ffd7dddf939e85de7b680@news.povray.org...
> "Bob" <omniverse*charter!net> wrote:
>> Brings up a question of color that's more often than not been a 
>> frustration
>> of mine. The orange looks brown... or more precisely, it looks like a tea
>> drink.
>> Many times I tried to get a traffic cone fluorescent orange color and
>> failed. Even if the color can be attained alone, any scene change 
>> (lighting,
>> etc.) is almost sure to lose the bright orange color. That seems to go 
>> for
>> yellow sometimes, too.
>
> I read that it has to do with the way our eyes interpret the combination 
> of red
> and green phosphors.  I can't remember where, though.  Normally I'd take 
> care
> of the problem by boosting the finish ( diffuse } value, but this won't 
> work
> with glass.

Maybe you could try increasing color beyond 1, like Clipka was saying. I 
realize there's probably ways to eventually attain some desired color 
needed, but what typically causes me trouble is simply typing something up 
and not getting the expected result. I was just expressing that here, not 
meaning to hijack your rendered rainbow pics.
;)
Just now trying for that elusive orange and got this:

sphere {
  0, 1
  texture {
    pigment {
      radial
      frequency 2
      color_map {
        [0.1 color rgb <1.0,0.0,0.0> ]
        [0.2 color rgb <1.0,0.1,0.01>*1.5 ]
        [0.3 color rgb <1.0,0.1,0.01>*1.5 ]
        [0.4 color rgb <1.0,1.0,0.0> ]
        [0.5 color rgb <1.0,1.0,0.0> ]
        [0.6 color rgb <0.0,1.0,0.0> ]
        [0.7 color rgb <0.0,1.0,0.0> ]
        [0.8 color rgb <0.0,0.0,1.0> ]
        [0.9 color rgb <0.0,0.0,1.0> ]
        [1.0 color rgb <1.0,0.0,1.0> ]
      }
      triangle_wave
    }
    finish{
   // ambient 0.1 diffuse 1.5
    }
  }
  rotate 45*y
  translate <0,0,3>
}

light_source {<30, 30, -30>,1}

Which, as you can see, is a very red color with very little blue. In lieu of 
a finish tweak I went with increased color values, as was said by Clipka. 
Used in a scene might be another matter, anyway this is what I'm thinking of 
as orange (if anybody renders this and sees the same). Orange as in 
tree-borne fruit, if not traffic cone orange?

Oh, and I also liked the ceramic rainbow... just not as much as glass with 
all its play of light.

Bob


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