POV-Ray : Newsgroups : povray.advanced-users : Extracting information from an existing color_map : Re: Extracting information from an existing color_map Server Time
1 Mar 2024 15:24:58 EST (-0500)
  Re: Extracting information from an existing color_map  
From: William F Pokorny
Date: 18 Feb 2023 06:27:40
Message: <63f0b62c$1@news.povray.org>
On 2/15/23 14:52, Bald Eagle wrote:
> With regard to the recent discussions about color_maps,  I was wondering if it
> were possible to somehow extract the number, or even the values of the entries
> in a color_map.
> 
> I know that we cannot do this directly, but I was wondering if there were
> perhaps a method by which a function could be applied which would reveal the
> locations of the "nodes".  Some discontinuity or eigenvector, or other clever
> exploit.
> 
> Perhaps there's a way to look at some sort of plot of the rgb values and see
> where the blending transitions from interpolating A into B  over to where it
> switches into interpolating B into C....
> 
> I'm also wondering if there is a color_map that exceeds the valid 0-1 span, if
> it were possible to access those invalid entries using the same sort of hacking
> strategy.
> 

Hi Bill,
I'm not keeping up well with this thread, but I have a couple thoughts.

---

Remember v3.8 supports color_map blend_mode and blend_gamma modifiers 
which are internal to the color_map definition. These can skew the 
overall color_map behavior.

#declare ColorMap01 = color_map {
     blend_mode 3 blend_gamma 2.5
     [0.000000 ...]
...
}

---

On accessing color_map values out of 'accessible' range(a) we need 
updated POV-Ray source. This has been implemented in my povr fork and 
was discussed back in 2019 here (though you completely hijacked the 
thread for another useful bug/fix :-) ):

http://news.povray.org/povray.beta-test.binaries/thread/%3C5dab3f55%241%40news.povray.org%3E/

or

Message: <5dab3f55$1@news.povray.org>

Aside: The web hidden http://news.povray.org/povray.beta-test.binaries/ 
has other, older, povr fork and v4.0 idea related posts. For a time I 
was trying not to confuse web news readers with povr things by using a 
group visible only via a tool like Thunderbird. On the git master branch 
becoming the v4.0 one in 2021, I started posting ideas in the v4.0 forum.

Bill P.

(a) As you know, the *_map mechanism in POV-Ray itself has long 
supported  key/index values well outside the [0-1] range, but we cannot 
make use of this in any official POV-Ray release due other internal 
limitations.


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