High!

As announced yesterday, I started experimenting with various radiosity 
and/or finish settings to get rid of the unrealistically dark surfaces 
inside the buildings... I'm quite aware that, on a bright sunny day, the 
outside environment is orders of magnitude brighter than rooms 
indirectly lit - but, on the other hand, the human eye's perception of 
brightness levels is logarithmic rather than linear, i. e. indoor scenes 
appear substantially brighter than they actually are.

But obviously PoV-Ray does not take this into account when rendering 
such indoor scenes... or is there a way to calibrate PoV-Ray's lighting 
system to match the human perception more closely?

I tried three combinations of radiosity brightness and diffuse values of 
the used texture, attached here (currently, beside the sand-coloured 
ground texture, only a simple "concrete" texture is used), but none of 
them satisfied me. What concerns me most is the stark contrast between 
the floor (lit by the blue sky) and the walls (lit only by the floor).

Is it possible to get more balanced (and, overall, higher) brightness 
levels with different radiosity values - or do I have to used some 
shadowless fill light(s)?

See you on www.khyberspace.de!

Yadgar

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Attachments:
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Preview of image '.jpg'

Preview of image '.jpg'

Preview of image '.jpg'

> But obviously PoV-Ray does not take this into account when rendering
> such indoor scenes... or is there a way to calibrate PoV-Ray's lighting
> system to match the human perception more closely?

You don't want to do that, because when your eye looks at the monitor/print 
out obviously it will do it's logarithmic processing again, so you'll get it 
twice and it will look weird.  Try taking a photo of the view you want with 
the exposure you want, and getting your POV generated image to match.

IME the most important thing is to get the ratio between sun brightness and 
sky brightness correct.  Once you have that sorted then everything else will 
just work, and you can scale the sun and sky brightness equally to get 
different exposures (eg for indoor scenes or outdoor scenes).  Again, you 
can check the ratio by comparing sunlit/shadow parts of your rendering with 
a photo.

Buy.

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> High!
> 
> As announced yesterday, I started experimenting with various radiosity 

> and/or finish settings to get rid of the unrealistically dark surfaces 

> inside the buildings... I'm quite aware that, on a bright sunny day, th
e 
> outside environment is orders of magnitude brighter than rooms 
> indirectly lit - but, on the other hand, the human eye's perception of 

> brightness levels is logarithmic rather than linear, i. e. indoor scene
s 
> appear substantially brighter than they actually are.

It depends on what settings you are already using, but have you tried 
increasing the recursion_limit so the light will bounce around in the 
rooms more and light up th walls?

-- 
-The Mildly Infamous Blue Herring

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scott skrev:
>> But obviously PoV-Ray does not take this into account when rendering
>> such indoor scenes... or is there a way to calibrate PoV-Ray's lighting
>> system to match the human perception more closely?
> 
> You don't want to do that, because when your eye looks at the
> monitor/print out obviously it will do it's logarithmic processing
> again, so you'll get it twice and it will look weird.  Try taking a
> photo of the view you want with the exposure you want, and getting your
> POV generated image to match.

No, there is a difference between looking at a scene like that in real
life, where the outdoor brightness is very high, and looking at a photo
of the same scene. The brightness of the brightest parts of the photo
depend on the light source illuminating the photo, in the same way that
looking at a photo of the sun is not as dangerous as looking into the sun.

/martin

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>> You don't want to do that, because when your eye looks at the
>> monitor/print out obviously it will do it's logarithmic processing
>> again, so you'll get it twice and it will look weird.  Try taking a
>> photo of the view you want with the exposure you want, and getting your
>> POV generated image to match.
>
> No, there is a difference between looking at a scene like that in real
> life, where the outdoor brightness is very high, and looking at a photo
> of the same scene. The brightness of the brightest parts of the photo
> depend on the light source illuminating the photo, in the same way that
> looking at a photo of the sun is not as dangerous as looking into the sun.

Well of course a photo is limited to reflecting 100% of the incident light, 
and a monitor to its maximum brightness, but that wasn't my point.  My point 
was that you shouldn't take into account the eyes processing in your image, 
because then it's not going to look realistic.  You should aim to create an 
image where the relative brightnesses match what is in real life.  You don't 
need to worry about how your eye works, just match real life and it will 
look realistic.

Comparing your rendering with a digital photo is a good way to do this, as 
most people don't have access to expensive brightness measurement equipment. 
It also means you don't have to worry about gamma of your display device, 
just match your output pixel values to the values in the photo.

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>
> Well of course a photo is limited to reflecting 100% of the incident light,
> and a monitor to its maximum brightness, but that wasn't my point.  My point
> was that you shouldn't take into account the eyes processing in your image,
> because then it's not going to look realistic.  You should aim to create an
> image where the relative brightnesses match what is in real life.  You don't
> need to worry about how your eye works, just match real life and it will
> look realistic.
>


You've confused realistic with photo-realistic. If you match a photo it will
look like a photo --- and photos have all the same problems he's listing. Take
a picture of a window on a sunny day, and the window sill, the wall around it,
and anything else will be very dark --- or else everything outside the window
will be over exposed. Real life doesn't have those problems because our eyes
are amazing.

A rendering with logartithmic light recording wouldn't look like a normal photo
--- it would look like a tone-mapped HDR image:
http://en.wikipedia.org/wiki/Tone_mapping . And for preserving detail the way a
memory does, it will be more effective.

The fast solution would be to use megapov to render to HDR and then use 3rd
party tone-mapping software.

-S

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High!

(sorry for the three-day delay, but meanwhile, my primary master 
harddisk crashed and I still have a pretty hard time to get the system 
working again... this posting is sent to you using a provisional 
installation running from a Sidux livedisk - Linux rules!)

scott schrieb:
> You don't want to do that, because when your eye looks at the 
> monitor/print out obviously it will do it's logarithmic processing 
> again, so you'll get it twice and it will look weird.  Try taking a 
> photo of the view you want with the exposure you want, and getting your 
> POV generated image to match.

Unfortunately, I don't (yet) own such a sophisticated camera... sounds 
strange from such an avid PoVghan, doesn't it? You know you've been 
raytracing for too long... when you never own less then five digital and 
chemical cameras just to get real-world lighting and radiosity levels right!

> IME the most important thing is to get the ratio between sun brightness 
> and sky brightness correct.  

Then probably my sun is too bright (and after dimming it down, the whole 
image has to be post-processed)...

See you in Khyberspace!

Yadgar

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> A rendering with logartithmic light recording wouldn't look like a normal 
> photo
> --- it would look like a tone-mapped HDR image:
> http://en.wikipedia.org/wiki/Tone_mapping . And for preserving detail the 
> way a
> memory does, it will be more effective.

Maybe so, but to me those tone-mapped images look far less like real life 
than a normal photo does.

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High!

Blue Herring schrieb:

> It depends on what settings you are already using, but have you tried 
> increasing the recursion_limit so the light will bounce around in the 
> rooms more and light up th walls?

Yes, meanwhile (after re-programming the whole scene, which was also 
lost in the harddisk crash last week) I increased recursion_limit up to 
20, but that won't either do the trick - see attached image!

See you in Khyberspace!

Yadgar

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Attachments:
Download '2008-07-31 inside my apartment, take 1 (yadgar).jpg' (15 KB)

Preview of image '2008-07-31 inside my apartment, take 1 (yadgar).jpg'

=?ISO-8859-15?Q?J=F6rg_=27Yadgar=27_Bleimann?= <yaz### [at] gmxde> wrote:
> High!
>
> Blue Herring schrieb:
>
> > It depends on what settings you are already using, but have you tried
> > increasing the recursion_limit so the light will bounce around in the
> > rooms more and light up th walls?
>
> Yes, meanwhile (after re-programming the whole scene, which was also
> lost in the harddisk crash last week) I increased recursion_limit up to
> 20, but that won't either do the trick - see attached image!
>
> See you in Khyberspace!
>
> Yadgar


I can see some artifacts that may be from your radiosity settings.  Can you post
your code?  If not, I recommend lowering your error bound to about 1/3 to 1/4 of
what it is.  Since a lot of the light is to be reflected from the bright, fully
lit corner, changing the error bound may increase the brightness in this case.
There are some other settings changes that I think you should consider also.




-Reactor

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