news: 3dfe1695@news.povray.org...
> Thanks I didn't think of that

Note that there are cases where I was never able to get rid of this problem,
in spite of putting "hollow" keywords everywhere, making sure that
everything was really transparent etc. I ended up rendering the leaves
separately and using a mask to put them on the final image !

G.


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In article <3dff75af@news.povray.org>,
 "Gilles Tran" <tra### [at] inapginrafr> wrote:

> Note that there are cases where I was never able to get rid of this problem,
> in spite of putting "hollow" keywords everywhere, making sure that
> everything was really transparent etc. I ended up rendering the leaves
> separately and using a mask to put them on the final image !

Probably because the transparent surface was causing POV to sample two 
shorter intervals instead of one long one. Raising the number of samples 
might have reduced or eliminated the artifact, at the cost of slower 
rendering.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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Gilles Tran wrote:

>news: 3dfe1695[at]news.povray.org...
>> Thanks I didn't think of that
>
>Note that there are cases where I was never able to get rid of this problem,
>in spite of putting "hollow" keywords everywhere, making sure that
>everything was really transparent etc. I ended up rendering the leaves
>separately and using a mask to put them on the final image !

A similar question:
I wanted to use a hollow transparent sphere to give some curvature
to my leaf image map, and it works great except when the transparent
part of the leaf's sphere intersects a (non-transparent) surface
behind it. I get black pixels, like it's showing coincident surfaces,
though the sphere's surface is transparent at that point.

I was thinking that I could use the image to clip the sphere somehow
(instead of a another sphere as I'm currently doing), but I wonder
if there is a simpler (and faster rendering) solution?

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In article <web.3dff7ff48a77e58da7778c0e0@news.povray.org>,
 "Renderdog" <slo### [at] hiwaaynet> wrote:

> I wanted to use a hollow transparent sphere to give some curvature
> to my leaf image map, and it works great except when the transparent
> part of the leaf's sphere intersects a (non-transparent) surface
> behind it. I get black pixels, like it's showing coincident surfaces,
> though the sphere's surface is transparent at that point.

If it is coincident with or intersects the surface, sometimes it will 
get hit first and the transmitted ray will miss the other surface, so 
you see the interior of the second object through the transparent one. 
Since the interior is in shadow, it is dark.

The only way to avoid this in the intersecting surface case would be to 
change the way POV handles non-refracting transparency.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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Christopher James Huff wrote:
> 
> In article <web.3dff7ff48a77e58da7778c0e0@news.povray.org>,
>  "Renderdog" <slo### [at] hiwaaynet> wrote:
> 
> > I wanted to use a hollow transparent sphere to give some curvature
> > to my leaf image map, and it works great except when the transparent
> > part of the leaf's sphere intersects a (non-transparent) surface
> > behind it. I get black pixels, like it's showing coincident surfaces,
> > though the sphere's surface is transparent at that point.
> 
> If it is coincident with or intersects the surface, sometimes it will
> get hit first and the transmitted ray will miss the other surface, so
> you see the interior of the second object through the transparent one.
> Since the interior is in shadow, it is dark.
> 
> The only way to avoid this in the intersecting surface case would be to
> change the way POV handles non-refracting transparency.

Or he may need to increase the max_trace_level in the global settings block
a bit.

-- 
Ken Tyler

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Ken wrote:
>
>Christopher James Huff wrote:
>>
>> If it is coincident with or intersects the surface, sometimes it will
>> get hit first and the transmitted ray will miss the other surface, so
>> you see the interior of the second object through the transparent one.
>> Since the interior is in shadow, it is dark.
>>
>> The only way to avoid this in the intersecting surface case would be to
>> change the way POV handles non-refracting transparency.
>
>Or he may need to increase the max_trace_level in the global settings block
>a bit.

My first suspect was max_trace_level, but increasing it didn't help. Looks
like I'll have to keep my objects away from the wall or not use transparency
and mask off the non-leaf parts.

Since the wall is an isosurface, perhaps increasing the accuracy would help,
or (if it's an option) maybe making the wall shadowless.

Thanks Christopher and Ken for your help.

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Renderdog wrote:
> 
> Ken wrote:
> >
> >Christopher James Huff wrote:
> >>
> >> If it is coincident with or intersects the surface, sometimes it will
> >> get hit first and the transmitted ray will miss the other surface, so
> >> you see the interior of the second object through the transparent one.
> >> Since the interior is in shadow, it is dark.
> >>
> >> The only way to avoid this in the intersecting surface case would be to
> >> change the way POV handles non-refracting transparency.
> >
> >Or he may need to increase the max_trace_level in the global settings block
> >a bit.
> 
> My first suspect was max_trace_level, but increasing it didn't help. Looks
> like I'll have to keep my objects away from the wall or not use transparency
> and mask off the non-leaf parts.
> 
> Since the wall is an isosurface, perhaps increasing the accuracy would help,
> or (if it's an option) maybe making the wall shadowless.
> 
> Thanks Christopher and Ken for your help.

How do you create an alpha channel?  Can POV do it?  Or do you need to
use a picture editor?

Thanks.

-- 
Tom A.
"Archie!  You are headstrong.  I am imperious.  It's a miracle 
we get along as well as we do." - Nero Wolf
Deja mail is gone.  Look for me at raugost at yahoo . com

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Tom A. wrote:

>How do you create an alpha channel?  Can POV do it?  Or do you need to
>use a picture editor?

To create a transparent image map, I use in indexed gif file and:

 transmit -index number-, 1.0

to make that color 100% transparent.

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Renderdog wrote:
> 
> Tom A. wrote:
> 
> >How do you create an alpha channel?  Can POV do it?  Or do you need to
> >use a picture editor?
> 
> To create a transparent image map, I use in indexed gif file and:
> 
>  transmit -index number-, 1.0
> 
> to make that color 100% transparent.

So, the code would be something like:

  sphere{<0,0,0>,1
    pigment{
      image_map {
        gif "world.gif"
        map_type 1
         transmit 0, 1.0
      }
    }
  }

(he asks from a PC without most of his usual graphics programs)?

-- 
Tom A.
"Archie!  You are headstrong.  I am imperious.  It's a miracle 
we get along as well as we do." - Nero Wolf
Deja mail is gone.  Look for me at raugost at yahoo . com

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Tom A. wrote:

>So, the code would be something like:
>
>  sphere{<0,0,0>,1
>    pigment{
>      image_map {
>        gif "world.gif"
>        map_type 1
>         transmit 0, 1.0
>      }
>    }
>  }
>
>(he asks from a PC without most of his usual graphics programs)?

Yes. Though you've probably tried it by now...

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