Hey all,

I made a couple of images (see povray.binaries.images post of the same name)
showing an odd result of using transparency.  The first image shows a
transparent object (merge of a box and a cylinder... pigment {rgbf
<0.9,0.9,0.9,0.9>}) on a plane.  The second image is just like the first
except it uses a spotlight instead of a point light.  The problem is the
plane (and green bar) in the distance... it is much more visible as seen
thru the transparent object than it is on the sides of the image.  I
rendered it in official 3.1 and the effect was there, but to a much lesser
extent.  Is this a bug???

Eric
--------------------
http://www.datasync.com/~ericfree
--------------------
"I don't like it, and I'm sorry I ever had anything to do with it."
- Erwin Schrodinger talking about Quantum Mechanics.

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"Eric Freeman" <eri### [at] datasynccom> wrote in message
news:38d7b5a1$1@news.povray.org...
| I made a couple of images (see povray.binaries.images post of the same name)
| showing an odd result of using transparency.  The first image shows a
| transparent object (merge of a box and a cylinder... pigment {rgbf
| <0.9,0.9,0.9,0.9>}) on a plane.  The second image is just like the first
| except it uses a spotlight instead of a point light.  The problem is the
| plane (and green bar) in the distance...

The pigment was raised to 0.98 (as stated in your 2nd message at p.b.i.) and it
was okay then, am I understanding this right?  If that's all then it's a very
nearly clear texture whereas before it was not.  Anyway, it's always seemed to
me that semi-transparent textures ('transmit' especially and visible spotlights
such as through the old 'atmosphere' of v3.0*) shouldn't be brightening the
background.  But I still have not checked this against reality very well.  Now
media is easy to darken the backgrounds of visible spotlights by using
'absorption' so that's not a problem anymore.  Textures on the other hand might
still be doing this.

Bob

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I think that it's a somewhat illusionary effect but is most likely related
to gamma correction.  Some people have complained about similar 'problems'
with scattering media.  It is caused by diffuse light bouncing off of the
glass being added to the transmitted light that comes through the glass.

Also, if the description of your material does not conserve energy (if
reflected light, including diffuse, phong, etc, plus transmitted light adds
up to more than 1.0) then you could run into problems like this.

There really shouldn't be any difference between MegaPov and the official
version, though.

-Nathan

Eric Freeman <eri### [at] datasynccom> wrote...
> Hey all,
>
> I made a couple of images (see povray.binaries.images post of the same
name)
> showing an odd result of using transparency.  The first image shows a
> transparent object (merge of a box and a cylinder... pigment {rgbf
> <0.9,0.9,0.9,0.9>}) on a plane.  The second image is just like the first
> except it uses a spotlight instead of a point light.  The problem is the
> plane (and green bar) in the distance... it is much more visible as seen
> thru the transparent object than it is on the sides of the image.  I
> rendered it in official 3.1 and the effect was there, but to a much lesser
> extent.  Is this a bug???
>
> Eric
> --------------------
> http://www.datasync.com/~ericfree
> --------------------
> "I don't like it, and I'm sorry I ever had anything to do with it."
> - Erwin Schrodinger talking about Quantum Mechanics.
>
>
>

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"Nathan Kopp" <Nat### [at] Koppcom> wrote in message
news:38d7dc0b$1@news.povray.org...
>
> I think that it's a somewhat illusionary effect but
> is most likely related to gamma correction.

I think you're right.  I made a larger image and the effect was almost
unnoticable... playing with my monitor's controls helped, too.

> Some people have complained about similar
> 'problems' with scattering media.  It is caused
> by diffuse light bouncing off of the glass being
> added to the transmitted light that comes
> through the glass.
>
> Also, if the description of your material does not
> conserve energy (if reflected light, including diffuse,
> phong, etc, plus transmitted light adds up to more
> than 1.0) then you could run into problems like this.

The complete texture was:

  $ GlassMat = material {
    texture {
      pigment {rgbf <0.9,0.9,0.9,0.9>}
      finish {reflection 0}
    }
  }

reflection 0 was added after I noticed the effect to see if the visible
floor plane in the "glass" was in front of or behind the glass.  It didn't
make a difference in the image.

Eric
--------------------
http://www.datasync.com/~ericfree
--------------------
"I don't like it, and I'm sorry I ever had anything to do with it."
- Erwin Schrodinger talking about Quantum Mechanics.

Post a reply to this message

I used transparency in one of my scenes and renderd it in Povray and
MegaPov. When I looked at the result I saw a only a white box in the Megapov
rendering. I shortend my scene up and here it is:
(In Povray all will remain black and in Mega box you see a white transparent
box)
#include "colors.inc"
camera{ location <4, 3,-6> look_at  <0, 0,  0>}
light_source
{
  0*x
  color rgb <1,1,1>
  spotlight
  cylinder
  translate <15,25,-15>
  point_at  <0,0,0>
  radius 200
  tightness 10
  falloff 180
}
box{<-1.5,-.5,1.5>, <-.5,.5,.5> pigment{color rgbt<1,1,1,.999>}}

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Vali <val### [at] gmxat> wrote...
> I used transparency in one of my scenes and renderd it in Povray and
> MegaPov. When I looked at the result I saw a only a white box in the
Megapov
> rendering. I shortend my scene up and here it is:

This appears to be a problem with the cylinder light source in MegaPov.  The
cylinder for some reason is very overpowering, so that even when you have
0.001 effective diffuse, you will still get a lot of diffused light.  If you
comment out "cylinder" from the light source, then you will get what you
expect.

-Nathan

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In order to keep the cylindrical light source try dropping to 'tightness 5'
instead.  Why is the 'radius' larger than the 'falloff', mistake?

Bob

"Nathan Kopp" <Nat### [at] Koppcom> wrote in message
news:38e11ec8@news.povray.org...
|
| Vali <val### [at] gmxat> wrote...
| > I used transparency in one of my scenes and renderd it in Povray and
| > MegaPov. When I looked at the result I saw a only a white box in the
| Megapov
| > rendering. I shortend my scene up and here it is:
|
| This appears to be a problem with the cylinder light source in MegaPov.  The
| cylinder for some reason is very overpowering, so that even when you have
| 0.001 effective diffuse, you will still get a lot of diffused light.  If you
| comment out "cylinder" from the light source, then you will get what you
| expect.
|
| -Nathan
|
|

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I just tested it and ...... it worked.
Nathan Kopp <Nat### [at] Koppcom> schrieb in im Newsbeitrag:
38e11ec8@news.povray.org...
>
> Vali <val### [at] gmxat> wrote...
> > I used transparency in one of my scenes and renderd it in Povray and
> > MegaPov. When I looked at the result I saw a only a white box in the
> Megapov
> > rendering. I shortend my scene up and here it is:
>
> This appears to be a problem with the cylinder light source in MegaPov.
The
> cylinder for some reason is very overpowering, so that even when you have
> 0.001 effective diffuse, you will still get a lot of diffused light.  If
you
> comment out "cylinder" from the light source, then you will get what you
> expect.
>
> -Nathan
>
>

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