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From: Cousin Ricky
Subject: Diffuse albedo and radiosity
Date: 8 Jul 2012 21:30:00
Message: <web.4ffa333d160b252f85de7b680@news.povray.org>
The sphere on the left uses diffuse 0.6.
The sphere on the right uses diffuse albedo 0.6.

Does this mean that when we're /not/ using radiosity, we should adjust the
ambient accordingly?


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albedo_radb-montage.png


 

From: clipka
Subject: Re: Diffuse albedo and radiosity
Date: 8 Jul 2012 21:47:51
Message: <4ffa3847$1@news.povray.org>
Am 09.07.2012 03:26, schrieb Cousin Ricky:
> The sphere on the left uses diffuse 0.6.
> The sphere on the right uses diffuse albedo 0.6.
>
> Does this mean that when we're /not/ using radiosity, we should adjust the
> ambient accordingly?

Something strange is happening there.
Are you using radiosity in the scene?

I didn't think about it when I implemented the albedo for diffuse, but 
it won't play nice with radiosity. Because radiosity actually doesn't 
support brilliance, and always computes diffuse illumination from other 
objects as if the surface had brilliance 1.0.


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From: Cousin Ricky
Subject: Re: Diffuse albedo and radiosity
Date: 8 Jul 2012 22:10:00
Message: <web.4ffa3cc9e507305985de7b680@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Are you using radiosity in the scene?

Yes, I am.


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From: Zeger Knaepen
Subject: Re: Diffuse albedo and radiosity
Date: 9 Jul 2012 09:39:37
Message: <4ffadf19$1@news.povray.org>
On 9/07/2012 3:47, clipka wrote:
> I didn't think about it when I implemented the albedo for diffuse, but
> it won't play nice with radiosity. Because radiosity actually doesn't
> support brilliance, and always computes diffuse illumination from other
> objects as if the surface had brilliance 1.0.

Is there a reason for that, other than speed?


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From: clipka
Subject: Re: Diffuse albedo and radiosity
Date: 9 Jul 2012 11:25:25
Message: <4ffaf7e5$1@news.povray.org>
Am 09.07.2012 15:39, schrieb Zeger Knaepen:
> On 9/07/2012 3:47, clipka wrote:
>> I didn't think about it when I implemented the albedo for diffuse, but
>> it won't play nice with radiosity. Because radiosity actually doesn't
>> support brilliance, and always computes diffuse illumination from other
>> objects as if the surface had brilliance 1.0.
>
> Is there a reason for that, other than speed?

Yes: Algorithm design, and the simple fact that nobody ever seriously 
cared about brilliance in radiosity scenes before.

Radiosity samples only store the level of illumination, but no 
information about the direction(s) from which this illumination comes. 
But this information is vital for the brilliance feature.

Storing detailed information about the individual illumination intensity 
from all the sampled directions is obviously an absolute no-go for 
memory reasons.

The issue could be addressed by taking brilliance into account when 
averaging the individual illumination intensities for one sample, and 
storing the information for which brilliance the sample was taken; the 
sample would then not be taken into account for textures with different 
brilliance values.


Another possible approach would be to store the illumination intensity 
not as a scalar but as spherical harmonics, which is essentially an 
efficient way of storing a blurred "image" of the illumination pattern. 
This could then be used to compute angle-dependent effects when re-using 
a sample rather than at gathering time. As an added benefit this could 
then also be used for handling perturbed normals without significant 
memory & speed penalty (currently extra samples are taken for this), and 
might also significantly improve the quality of cylindrical surfaces at 
little extra cost. It's an idea I've already pondered for future 
versions of POV-Ray, but I'll have to dive deep into spherical harmonics 
math for that.


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From: Zeger Knaepen
Subject: Re: Diffuse albedo and radiosity
Date: 10 Jul 2012 07:10:58
Message: <4ffc0dc2$1@news.povray.org>
> Yes: Algorithm design, and the simple fact that nobody ever seriously
> cared about brilliance in radiosity scenes before.

Well, I did notice a "rubberlike" quality in all radiosity-lit scenes 
though, now I know why :)


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From: James Holsenback
Subject: Re: Diffuse albedo and radiosity
Date: 10 Jul 2012 07:57:36
Message: <4ffc18b0@news.povray.org>
On 07/08/2012 09:47 PM, clipka wrote:
> Am 09.07.2012 03:26, schrieb Cousin Ricky:
>> The sphere on the left uses diffuse 0.6.
>> The sphere on the right uses diffuse albedo 0.6.
>>
>> Does this mean that when we're /not/ using radiosity, we should adjust
>> the
>> ambient accordingly?
>
> Something strange is happening there.
> Are you using radiosity in the scene?
>
> I didn't think about it when I implemented the albedo for diffuse, but
> it won't play nice with radiosity. Because radiosity actually doesn't
> support brilliance, and always computes diffuse illumination from other
> objects as if the surface had brilliance 1.0.

what about having albedo for diffuse ignored if radiosity is used ... 
I've ran into this problem  as well. Thanks to the OP for bringing this 
up, I had forgotten about it working on other higher priority stuff. If 
a change is not possible perhaps a "Note" in the docs will suit until a 
better idea comes along ;-)


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From: clipka
Subject: Re: Diffuse albedo and radiosity
Date: 10 Jul 2012 08:06:26
Message: <4ffc1ac2$1@news.povray.org>
Am 10.07.2012 13:57, schrieb James Holsenback:

>> I didn't think about it when I implemented the albedo for diffuse, but
>> it won't play nice with radiosity. Because radiosity actually doesn't
>> support brilliance, and always computes diffuse illumination from other
>> objects as if the surface had brilliance 1.0.
>
> what about having albedo for diffuse ignored if radiosity is used ...
> I've ran into this problem  as well. Thanks to the OP for bringing this
> up, I had forgotten about it working on other higher priority stuff. If
> a change is not possible perhaps a "Note" in the docs will suit until a
> better idea comes along ;-)

A change is definitely possible; I'll probably go for ignoring the 
albedo correction factor only for radiosity computations.


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From: clipka
Subject: Re: Diffuse albedo and radiosity
Date: 10 Jul 2012 08:41:26
Message: <4ffc22f6@news.povray.org>
Working on the fix.

Back row: using "diffuse 0.3"
Front row: using "diffuse albedo 0.3"

 From left to right: Brilliance 10, 1, 0.1

First image: RC6
Second image: With fix

(Note that this fix will only work with the "albedo" keyword, /not/ a 
manually corrected diffuse value using the "VooDoo formula".)


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Attachments:
Download 'albedo_radiosity_diffuse_rc6.png' (186 KB) Download 'albedo_radiosity_diffuse_fix.png' (187 KB)

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albedo_radiosity_diffuse_rc6.png

Preview of image 'albedo_radiosity_diffuse_fix.png'
albedo_radiosity_diffuse_fix.png


 

From: Cousin Ricky
Subject: Re: Diffuse albedo and radiosity
Date: 10 Jul 2012 16:45:00
Message: <web.4ffc932ae507305985de7b680@news.povray.org>
James Holsenback <nom### [at] nonecom> wrote:
> what about having albedo for diffuse ignored if radiosity is used ...

Sounds reasonable.


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