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> Hello,
>
> I'm trying to create an image with scattering media, on a white background. This
> topic seems to be similar to that posted by someone in 2002
>
(http://news.povray.org/povray.general/thread/%3CXns92C3BC15D86CCseed7%40povray.org%3E/),
> but I did not see a solution in that thread.
>
> I can create the image I want with no problem with a BLACK background (see this
> image: http://tinypic.com/r/1sh8gw/6). While my input *pov file is rather large,
> below are the (I think) essential elements of creating that image:
> ---------------------------------------
> #declare color_light = rgb <2.00, 2.00, 2.00>;
> #declare color_background = rgb <0.00, 0.00, 0.00>;
>
> light_source { light_location color color_light media_interaction off shadowless
> scale light_scale }background { color color_background }
>
> light_source { <80, 15.516/2, 65.259> color color_light spotlight point_at <5*43
> ..628/6., 15.516/2, 65.259/2> radius 10 falloff 5 tightness 20 media_attenuation
> on}
>
> box {
> <0, 0, 0>, <80, 15.51625, 80>
> texture {pigment { color rgbt <1,1,1,1>}} hollow interior { media {scattering
> {1, 0.07 extinction 0.01} intervals 5 samples 300,300}}}
>
> ---------------------------------------------
>
> I wanted to make a white background, so I made color_background rgb < 1,1,1> and
> then tried to modify the spotlight light_source by setting the spotlight color
> to something like red. However, this is what the outputted image looks like in
> this case: http://tinypic.com/r/10prshz/6.
>
> You can see in that image that there is some-sort of red spotlight action going
> on, in that the atomic positions in the spotlight have some mixture of red color
> on them, but definitely the image does not have the scattering effects present
> with the white background.
>
> What am I missing? Thanks for any pointers you can give.
>
> Best,
> Brad
>
>
Your media seems to comform to the obsolete sampling method 1. The
default is method 3. With that method, the followings apply:
Your media will render faster if you omit intervals 5. It default to
intervals 1 and should be left alone. For example, intervals 1 samples
1000 renders faster than intervals 10 samples 20 for 5 times as many
samples.
Also, the second samples parameter is NOT used.
Against a white background, the colouring can easily get drowned out,
especialy when using a very smal extinction value. Remove extinction
0.01 and use the default of 1. This will darken the background.
For all light_source, "media_atenuation" defaults to ON, no need to set it.
As other pointed out, you can use absorbing media.
You can also use a background that is not totaly white.
Scaling a light is the same as multiplying it's location by the scale value.
Alain
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> Alain <kua### [at] videotron ca> wrote:
>
>>
>> For all light_source, "media_atenuation" defaults to ON, no need to set it.
>
> Really? If so, I didn't know that. But the docs for "Atmospheric Attenuation"
> say this:
> "Normally light coming from light sources is not influenced by fog or
> atmospheric media. This can be changed by turning the media_attenuation on for a
> given light source on."
>
> Or did you mean media *interaction*? That DOES default to ON.
>
>
>
fog YES. fog never cause light atenuation. Regular absorbing and
scattering media, contained or not, always intract with your lights
unless you explicitely set media_attenuation off.
It may be another leftover from some early versions, like no later than
version 3.0, maybe version 2...
My first brush with scattering media date back to version 3.1, and I got
shadows from media as well as media self-shadowing. I've NEVER used
"media_atenuation on" and all my scattering medias cast shadows unless I
set extinction to zero.
In the same optic, ALL light_source, except shadowless ones, have this
default photons block:
photons{refraction on difraction on area_light off}
The documentations erroneously tell it's all OFF.
Alain
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