In Norbert Kern's Bluebell Wood discussion, there was mention of the use 
of basckside illumination by Alain and myself. Here is an example of its 
use, a 2019 update of a 2012 scene from the Iskander/Gancaloon universe.
Backside illumination was applied to the curtains.

-- 
Thomas

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Thomas de Groot <tho### [at] degrootorg> wrote:
> In Norbert Kern's Bluebell Wood discussion, there was mention of the use
> of basckside illumination by Alain and myself. Here is an example of its
> use, a 2019 update of a 2012 scene from the Iskander/Gancaloon universe.
> Backside illumination was applied to the curtains.
>
> --
> Thomas

I have not yet used backside illumination, so I'm curious as to what I should
see in your scene. I assume that the curtain objects themselves are
semi-transparent(?), and that the effect is seen as the small triangular light
patches on the left-side curtain?

So many tricks to learn, so little time ;-)

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Am 22.11.2020 um 16:22 schrieb Kenneth:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> In Norbert Kern's Bluebell Wood discussion, there was mention of the use
>> of basckside illumination by Alain and myself. Here is an example of its
>> use, a 2019 update of a 2012 scene from the Iskander/Gancaloon universe.
>> Backside illumination was applied to the curtains.
>>
>> --
>> Thomas
> 
> I have not yet used backside illumination, so I'm curious as to what I should
> see in your scene. I assume that the curtain objects themselves are
> semi-transparent(?), and that the effect is seen as the small triangular light
> patches on the left-side curtain?
> 
> So many tricks to learn, so little time ;-)
> 
> 
> 
As all I know, backside illumination and semi transparency is not the 
same. Semi transparency can be achieved by using an alpha-channel within 
a png-based texture. Backside illumination is a special calculation of 
diffuse reflections.

I used
      finish { diffuse albedo 0.55,0.4 }
in this image:
      http://news.povray.org/5f2ae26d%40news.povray.org
at all of the balloons.

As I understand it, it means that 55 % of the light from front 
lightsources is diffuse reflected and that 40 % of light from sources at 
the backside of an object can pass through.

Best regards
Michael

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> Am 22.11.2020 um 16:22 schrieb Kenneth:
>> Thomas de Groot <tho### [at] degrootorg> wrote:
>>> In Norbert Kern's Bluebell Wood discussion, there was mention of the use
>>> of basckside illumination by Alain and myself. Here is an example of its
>>> use, a 2019 update of a 2012 scene from the Iskander/Gancaloon universe.
>>> Backside illumination was applied to the curtains.
>>>
>>> -- 
>>> Thomas
>>
>> I have not yet used backside illumination, so I'm curious as to what I 
>> should
>> see in your scene. I assume that the curtain objects themselves are
>> semi-transparent(?), and that the effect is seen as the small 
>> triangular light
>> patches on the left-side curtain?
>>
>> So many tricks to learn, so little time ;-)
>>
>>
>>
> As all I know, backside illumination and semi transparency is not the 
> same. Semi transparency can be achieved by using an alpha-channel within 
> a png-based texture. Backside illumination is a special calculation of 
> diffuse reflections.
> 
> I used

> in this image:

> at all of the balloons.
> 
> As I understand it, it means that 55 % of the light from front 
> lightsources is diffuse reflected and that 40 % of light from sources at 
> the backside of an object can pass through.
> 
> Best regards
> Michael
> 
You understand correctly, with a little precision : The part that pass 
through does it diffusely.

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Op 22/11/2020 om 16:22 schreef Kenneth:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> In Norbert Kern's Bluebell Wood discussion, there was mention of the use
>> of basckside illumination by Alain and myself. Here is an example of its
>> use, a 2019 update of a 2012 scene from the Iskander/Gancaloon universe.
>> Backside illumination was applied to the curtains.
>>
>> --
>> Thomas
> 
> I have not yet used backside illumination, so I'm curious as to what I should
> see in your scene. I assume that the curtain objects themselves are
> semi-transparent(?), and that the effect is seen as the small triangular light
> patches on the left-side curtain?
> 
> So many tricks to learn, so little time ;-)
> 
> 
> 
Michael and Alain give the answer.

You will see the effect if you put two versions side by side, one with, 
one without the use of backside illumination (used indeed with a 
semi-transparant texture): without it, the aspect will be much more dull.

In my image, it it just the "shininess" of the curtain parts in sunlight 
that is increased making the whole more attractive but also more natural 
imo.

-- 
Thomas

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Thomas de Groot <tho### [at] degrootorg> wrote:

Thanks to all for the tips and explanations. Backside illumination is a feature
that I've always wanted to try, but I have not yet made a scene that would take
advantage of it.

> >
> Michael and Alain give the answer.
>
>
> In my image, it it just the "shininess" of the curtain parts in sunlight
> that is increased making the whole more attractive but also more natural
> imo.
>

Ah, I see.

And about those "small triangular patches" I mentioned: I see now that they are
the sails of another boat, behind the curtain! Duh. Sorry for the confusion.

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Op 24/11/2020 om 02:00 schreef Kenneth:
> And about those "small triangular patches" I mentioned: I see now that they are
> the sails of another boat, behind the curtain! Duh. Sorry for the confusion.
> 

LOL. I was puzzled about that indeed.

-- 
Thomas

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On 11/22/2020 2:46 AM, Thomas de Groot wrote:
> In Norbert Kern's Bluebell Wood discussion, there was mention of the use 
> of basckside illumination by Alain and myself. Here is an example of its 
> use, a 2019 update of a 2012 scene from the Iskander/Gancaloon universe.
> Backside illumination was applied to the curtains.
> 

Newsgroups need a "Like" feature.


Mike

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