POV-Ray : Newsgroups : povray.pov4.discussion.general : palette RGB values instead of index Server Time: 19 Feb 2019 23:17:33 GMT
  palette RGB values instead of index (Message 1 to 5 of 5)  
From: Woody
Subject: palette RGB values instead of index
Date: 30 Aug 2012 22:25:01
Message: <web.503fe720c06b9598d9fdb3af0@news.povray.org>
This question is in regards to a post I made earlier today in the general forum
(See
http://news.povray.org/povray.general/thread/%3Cweb.503e0aa3d8fa7d9cd9fdb3af0%40news.povray.org%3E/)

Specifically it relates to the 'image_map' keyword and how 'filter' and
'transmit' colors are specified. Currently they are specified by integer values
that serve as index numbers. (See documentation at
http://www.povray.org/documentation/view/3.6.1/337/)

How hard would it be to make it so instead of requiring an index number, only
the RGB value of the color in question was needed?

For example instead of something like (as detailed at the above documentation
location)

 image_map {
    gif "mypic.gif"
    filter   0, 0.5 // Make color 0 50% filtered transparent
    filter   5, 1.0 // Make color 5 100% filtered transparent
    transmit 8, 0.3 // Make color 8 30% non-filtered transparent
  }

something like

 image_map {
    gif "mypic.gif"
    filter   <0,0,0>, 0.5
         // RGB value of color 0, make it 50% filtered transparent
    filter   <0,128,0>, 1.0
        // RGB value of color 5, make it 50% filtered transparent
    transmit <0,255,255>, 0.3
        // RGB value of color 8, make it 30% non-filtered transparent
  }

I'm assuming for such a convention that if the color is not present there is no
filter or transmit applied.

Any thoughts?

-Jeff


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From: clipka
Subject: Re: palette RGB values instead of index
Date: 31 Aug 2012 01:16:16
Message: <50401060$1@news.povray.org>
Am 31.08.2012 00:20, schrieb Woody:

> For example instead of something like (as detailed at the above documentation
> location)
>
>   image_map {
>      gif "mypic.gif"
>      filter   0, 0.5 // Make color 0 50% filtered transparent
>      filter   5, 1.0 // Make color 5 100% filtered transparent
>      transmit 8, 0.3 // Make color 8 30% non-filtered transparent
>    }
>
> something like
>
>   image_map {
>      gif "mypic.gif"
>      filter   <0,0,0>, 0.5
>           // RGB value of color 0, make it 50% filtered transparent
>      filter   <0,128,0>, 1.0
>          // RGB value of color 5, make it 50% filtered transparent
>      transmit <0,255,255>, 0.3
>          // RGB value of color 8, make it 30% non-filtered transparent
>    }
>
> I'm assuming for such a convention that if the color is not present there is no
> filter or transmit applied.
>
> Any thoughts?

Yes, this one: Why bother with old-fashioned GIF files anyway?


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From: Woody
Subject: Re: palette RGB values instead of index
Date: 31 Aug 2012 17:05:01
Message: <web.5040eddc4debb7e949b4acd50@news.povray.org>
>
> Yes, this one: Why bother with old-fashioned GIF files anyway?

I was just using the example given in the documentation to avoid coming up with
my own example. I suppose it could just as easily been a BMP, IFF or PNG file.

Are you suggessting requiring the PNG format and using its implied transperency
scheme?

-Jeff


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From: clipka
Subject: Re: palette RGB values instead of index
Date: 31 Aug 2012 20:38:25
Message: <504120c1$1@news.povray.org>
Am 31.08.2012 19:01, schrieb Woody:
>>
>> Yes, this one: Why bother with old-fashioned GIF files anyway?
>
> I was just using the example given in the documentation to avoid coming up with
> my own example. I suppose it could just as easily been a BMP, IFF or PNG file.
>
> Are you suggessting requiring the PNG format and using its implied transperency
> scheme?

Well, that's what I'd recommend, at any rate.

If you told us what you're actually trying to achieve, rather than what 
tool you happen to have in mind for that purpose, we might also be able 
to come up with a different approach to suit your needs.

The approach you suggests seems rather straightforward at first glance, 
but (A) I fail to see where it's actually of use, and (B) at second 
glance it actually turns out to be non-trivial not only to implement, 
but even more so to even specify in a consistent manner. For starters, 
you suggest to specify the color values in units from 0 to 255, instead 
of the 0.0 to 1.0 range used everywhere else throughout POV-Ray; but the 
trouble only barely begins there: Are these colors raw image values? 
Linear values? sRGB values? For consistency the colors should be 
interpreted as "cooked" to fit POV-Ray's color model (subject to 
assumed_gamma and all), but I suspect this would make the whole thing 
pretty pointless.


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From: Woody
Subject: Re: palette RGB values instead of index
Date: 4 Sep 2012 12:55:01
Message: <web.5045f95b4debb7e9d9fdb3af0@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Well, that's what I'd recommend, at any rate.
>
> If you told us what you're actually trying to achieve, rather than what
> tool you happen to have in mind for that purpose, we might also be able
> to come up with a different approach to suit your needs.
>
> The approach you suggests seems rather straightforward at first glance,
> but (A) I fail to see where it's actually of use, and (B) at second
> glance it actually turns out to be non-trivial not only to implement,
> but even more so to even specify in a consistent manner. For starters,
> you suggest to specify the color values in units from 0 to 255, instead
> of the 0.0 to 1.0 range used everywhere else throughout POV-Ray; but the
> trouble only barely begins there: Are these colors raw image values?
> Linear values? sRGB values? For consistency the colors should be
> interpreted as "cooked" to fit POV-Ray's color model (subject to
> assumed_gamma and all), but I suspect this would make the whole thing
> pretty pointless.

I can see your point.

The whole cause of this post had to do with a problem I was having. I had an
image with quite a few colors that were otherwise indistinguishable to the human
eye. Because of that, finding the index of the exact color I wanted to make
transparent would have been difficult.

But you are right, there are quite a few problems with that, and would be of
marginal benefit.

-Jeff


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