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On 1/25/2016 4:22 PM, clipka wrote:
>> Because it differs from the original image. Can I lower the density
>> without changing the color?
>
> I thought I had given a clear enough answer, but here it is again in a
> nutshell:
>
> Yes, you /can/ do that by reducing the "extinction" parameter. /But/
> tampering with the setting will void your warranty (read: break physical
> realism).
>
I've lowered extinction to 1/100000000 and it has zero effect. Here is
the code I am using now.
Mike
#declare atmos_material = material
{
texture {pigment {color rgbt 1}}
interior
{
media
{
scattering
{
4, rgb <0.2,0.4,1.0>/10000
extinction 1/100000000
}
samples 10
}
}
}
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Am 25.01.2016 um 22:15 schrieb Mike Horvath:
> On 1/25/2016 4:00 PM, Mike Horvath wrote:
>> Because it differs from the original image. Can I lower the density
>> without changing the color?
>>
>>
>> Mike
>
>
> Can I use a density statement? How do I make a density function that
> simply lowers the density to 1/10 everywhere?
Of course you can use a density statement -- you're already doing that.
To lower the density to 1/10 everywhere, all you need to do is divide
all the values in the color_map by 10 (but use rgb instead of srgb instead).
/But/ by lowering the density you not only make the background more
visible again -- you also reduce the scattering effect.
Think of it this way: If you reduce the density of a gas, you reduce the
probability that any given light ray hits a gas molecule and is diverted
from its original direction to a new one: Light en route to the camera
from the background has less chance of being diverted /away/ from the
camera, while light en route to anywhere in the scene from a light
source has less chance of being diverted /towards/ the camera.
I might also add that dividing the scattering media colour by 10 has
exactly the same effect as dividing the density values by 10.
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On 1/25/2016 4:37 PM, clipka wrote:
> Think of it this way: If you reduce the density of a gas, you reduce the
> probability that any given light ray hits a gas molecule and is diverted
> from its original direction to a new one: Light en route to the camera
> from the background has less chance of being diverted /away/ from the
> camera, while light en route to anywhere in the scene from a light
> source has less chance of being diverted /towards/ the camera.
I still don't understand why lowering the density of the gas darkens the
scene more than not having any media at all.
Mike
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Am 25.01.2016 um 22:35 schrieb Mike Horvath:
> On 1/25/2016 4:22 PM, clipka wrote:
>>> Because it differs from the original image. Can I lower the density
>>> without changing the color?
>>
>> I thought I had given a clear enough answer, but here it is again in a
>> nutshell:
>>
>> Yes, you /can/ do that by reducing the "extinction" parameter. /But/
>> tampering with the setting will void your warranty (read: break physical
>> realism).
>
> I've lowered extinction to 1/100000000 and it has zero effect. Here is
> the code I am using now.
Then I must confess I have no idea what you are talking about when you
say you want to "lower the density without changing the colour" because
it is "too dark" when "properly dense".
If extinction doesn't have any noticeable effect, it means that the "too
dark" effect you observe is not due to a lack of light from the
background getting through to the camera.
I must consequently assume that the "too dark" effect you observe is
instead due to a lack of light /scattered to/ the camera, but to get
more of this light you need a /higher/ density rather than a lower one.
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Am 25.01.2016 um 22:46 schrieb Mike Horvath:
> On 1/25/2016 4:37 PM, clipka wrote:
>> Think of it this way: If you reduce the density of a gas, you reduce the
>> probability that any given light ray hits a gas molecule and is diverted
>> from its original direction to a new one: Light en route to the camera
>> from the background has less chance of being diverted /away/ from the
>> camera, while light en route to anywhere in the scene from a light
>> source has less chance of being diverted /towards/ the camera.
>
> I still don't understand why lowering the density of the gas darkens the
> scene more than not having any media at all.
Are you absolutely sure it does, and you're not seeing the effect from
any other difference?
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On 1/25/2016 4:48 PM, clipka wrote:
> Am 25.01.2016 um 22:46 schrieb Mike Horvath:
>> On 1/25/2016 4:37 PM, clipka wrote:
>>> Think of it this way: If you reduce the density of a gas, you reduce the
>>> probability that any given light ray hits a gas molecule and is diverted
>>> from its original direction to a new one: Light en route to the camera
>>> from the background has less chance of being diverted /away/ from the
>>> camera, while light en route to anywhere in the scene from a light
>>> source has less chance of being diverted /towards/ the camera.
>>
>> I still don't understand why lowering the density of the gas darkens the
>> scene more than not having any media at all.
>
> Are you absolutely sure it does, and you're not seeing the effect from
> any other difference?
>
I've attached two renders. One is with no media at all. The other is
with the media, but the scattering color set to rgb 0.
Mike
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Attachments:
Download 'gh_scene_spinner_cutaway_e_no_media.png' (91 KB)
Download 'gh_scene_spinner_cutaway_e_zero_density.png' (77 KB)
Preview of image 'gh_scene_spinner_cutaway_e_no_media.png'
Preview of image 'gh_scene_spinner_cutaway_e_zero_density.png'
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Am 25.01.2016 um 22:56 schrieb Mike Horvath:
> On 1/25/2016 4:48 PM, clipka wrote:
>> Am 25.01.2016 um 22:46 schrieb Mike Horvath:
>>> On 1/25/2016 4:37 PM, clipka wrote:
>>>> Think of it this way: If you reduce the density of a gas, you reduce
>>>> the
>>>> probability that any given light ray hits a gas molecule and is
>>>> diverted
>>>> from its original direction to a new one: Light en route to the camera
>>>> from the background has less chance of being diverted /away/ from the
>>>> camera, while light en route to anywhere in the scene from a light
>>>> source has less chance of being diverted /towards/ the camera.
>>>
>>> I still don't understand why lowering the density of the gas darkens the
>>> scene more than not having any media at all.
>>
>> Are you absolutely sure it does, and you're not seeing the effect from
>> any other difference?
>
> I've attached two renders. One is with no media at all. The other is
> with the media, but the scattering color set to rgb 0.
This is seriously odd, entirely unexpected, and to my present knowledge
as a developer only explicable by a bug.
As I cannot reproduce the behaviour here with a simple scene, I would
kindly ask you to post some minimalistic version of your scene as an
attachment in povray.binary.scene-files so I can have a closer look at it.
Also, please let me know exactly which version of POV-Ray you are using.
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On 1/25/2016 4:46 PM, clipka wrote:
> I must consequently assume that the "too dark" effect you observe is
> instead due to a lack of light /scattered to/ the camera, but to get
> more of this light you need a /higher/ density rather than a lower one.
>
I found the problem. It had to do with the gas container object having
the same radius as the outer metal shell. When I increased the radius so
that the surfaces were not touching, the darkness went away and the
scene rendered normally.
Sorry for the trouble.
Mike
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Am 25.01.2016 um 23:15 schrieb Mike Horvath:
> On 1/25/2016 4:46 PM, clipka wrote:
>> I must consequently assume that the "too dark" effect you observe is
>> instead due to a lack of light /scattered to/ the camera, but to get
>> more of this light you need a /higher/ density rather than a lower one.
>
> I found the problem. It had to do with the gas container object having
> the same radius as the outer metal shell. When I increased the radius so
> that the surfaces were not touching, the darkness went away and the
> scene rendered normally.
Still a bit odd, but I guess the coincident surface problem can cause
any number of side effects.
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On 1/25/2016 5:35 PM, clipka wrote:
> Am 25.01.2016 um 23:15 schrieb Mike Horvath:
>> On 1/25/2016 4:46 PM, clipka wrote:
>>> I must consequently assume that the "too dark" effect you observe is
>>> instead due to a lack of light /scattered to/ the camera, but to get
>>> more of this light you need a /higher/ density rather than a lower one.
>>
>> I found the problem. It had to do with the gas container object having
>> the same radius as the outer metal shell. When I increased the radius so
>> that the surfaces were not touching, the darkness went away and the
>> scene rendered normally.
>
> Still a bit odd, but I guess the coincident surface problem can cause
> any number of side effects.
>
It would be cool if, instead of messing with the sizes of objects, you
could flag one or another object as dominant. I.e. when they touch, the
dominant object's textures take precedence.
Mike
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