POV-Ray : Newsgroups : irtc.stills : TC-RTC comments Server Time: 19 Dec 2018 11:11:27 GMT
  TC-RTC comments (Message 1 to 5 of 5)  
From: Thomas de Groot
Subject: TC-RTC comments
Date: 1 Sep 2008 12:37:22
Message: <48bbe202@news.povray.org>
The results are in and I am (happily) surprised to get a second place! 
Thanks to all!! And well done everybody!

I would like to take the opportunity to answer to some of the more technical 
comments to my scene, mainly because they address problems and puzzles that 
I do not know how to solve properly.

There are several comments about the rather flat shadows and the flatish 
contrast of the towers in the background. I know. And I wonder how to solve 
this. The truth is that there is only one (repeat: one) light source in this 
scene: the Sun. The luminosity (in Lightsys) has been multiplied by 3.5. 
There is no ambient finish used anywhere. No ambient occlusion. Radiosity 
uses the following settings:

    radiosity {
      //saving radiosity data:
      #if (RadSave)
        #debug "saving...\n"
        save_file "TS.rad"
        pretrace_start 0.1           // start pretrace at this size
        pretrace_end   0.0025           // end pretrace at this size
        error_bound 0.5                // higher -> smoother, less accurate 
[1.8]
        count 1000                     // higher -> higher quality (1..1600) 
[35]
        always_sample on            // turn sampling in final trace off [on]
        media off                     // take media into account [off]
        normal off                    // take surface normals into account 
[off]

      //reading radiosity data:
      #else
        #debug "reading...\n"
        load_file "TS.rad"
        pretrace_start 1
        pretrace_end 1
        error_bound 0.9                // higher -> smoother, less accurate 
[1.8]
        count 300                     // higher -> higher quality (1..1600) 
[35]
        always_sample off            // turn sampling in final trace off 
[on]
        media off                     // take media into account [off]
        normal off                    // take surface normals into account 
[off]
      #end

      //common settings:
      brightness 1                  // brightness of radiosity effects 
(0..1) [1]
      recursion_limit 2             // how much interreflections are 
calculated (1..5+) [3]
      nearest_count 6               // higher -> higher quality (1..10) [5]
      adc_bailout 0.005
      low_error_factor 0.8           // reduce error_bound during last 
pretrace step
      minimum_reuse 0.015           // reuse of old radiosity samples 
[0.015]
      gray_threshold 0.5            // increase for weakening colors (0..1) 
[0]
      //max_sample 1.0              // maximum brightness of samples
    }

I believe that better shadows would have been obtained with a higher 
recursion_limit. I experimented a bit and that seemed to be the case, but it 
increased render time a lot. Overall, I think radiosity is the culprit here 
and my trouble with using it correctly. Any comment on this is more than 
welcome.

Something that puzzles me is the bright *light* in the shadow on the right 
tower, as if the left tower reflected much light. Maybe that is the case? 
This did not happen in a no radiosity image.

Also, I am not happy about the rendering of the cobblestone texture in and 
out of the shadows. The shadowy parts are *motly*, which they are not in a 
no radiosity scene.

I wonder if I should not have used different lightgroups in this scene, 
separate for the foreground and the background...

Again, any comments on these issues are more than welcome!

Thomas


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From: Hildur K 
Subject: Re: TC-RTC comments
Date: 1 Sep 2008 16:00:00
Message: <web.48bc094ff7aedb2e80197cfe0@news.povray.org>
"Thomas de Groot" <t.d### [at] internlDOTnet> wrote:
> The results are in and I am (happily) surprised to get a second place!
> Thanks to all!! And well done everybody!
>
> I would like to take the opportunity to answer to some of the more technical
> comments to my scene, mainly because they address problems and puzzles that
> I do not know how to solve properly.
>
> There are several comments about the rather flat shadows and the flatish
> contrast of the towers in the background. I know. And I wonder how to solve
> this. The truth is that there is only one (repeat: one) light source in this
> scene: the Sun. The luminosity (in Lightsys) has been multiplied by 3.5.
> There is no ambient finish used anywhere. No ambient occlusion. Radiosity
> uses the following settings:

Hi Thomas, I like you image very much! Actually my favorite this round. But they
are right, it´s more flat that it needs to be.

When you say you are not using ambient finish I´m assuming you left them to the
default value. Which is 0.1 and therefore emitting light! So if you want to get
rid of ambient finish you have to write ambient 0 for every single material.
(My favorite is diffuse 0.9, ambient 0, looks realistic in most cases, except
for some metals maybe.)
If ambient is left to the default you lose the "shadows inside the shadow" if
you know what I mean.

Using a single light source like you did, is the best (only) approach in your
case, using
radiosity instead to take care of the shadow areas and should look great in
your image. What I´m trying to say is that you scene has a -great- potential
light wise.

It also seems that you are basing your radiosity settings on the default Pov
values which I have found fast but useless in most cases, the colors usually are
way to bright and saturated and everything looks flat and artificial.

I have a little tutorial on my site, if you haven´t seen it. Maybe the radiosity
settings there can be used as a base for you settings, even thought the
situation is somewhat different. They are originally
based on the Pov manual as the "best" but always have to be tweaked. Maybe you
should check it out.

http://www.simnet.is/hildurka/content/tut1page.htm

Also I don´t know what system your are using and if you have the patience to
wait on a slow render. But it´s usually worth the few extra hours (or days! ;)

Let me know if this doesn´t work for you, then I might be able to dig up some
radiosity settings from some outdoor scene which have worked in the past.


Hildur


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From: Thomas de Groot
Subject: Re: TC-RTC comments
Date: 2 Sep 2008 07:08:23
Message: <48bce667$1@news.povray.org>
"Hildur K." <hil### [at] 3dcafemailevery1net> schreef in bericht 
news:web.48bc094ff7aedb2e80197cfe0@news.povray.org...
>
> Hi Thomas, I like you image very much! Actually my favorite this round. 
> But they
> are right, it´s more flat that it needs to be.

Thank you Hildur!

> When you say you are not using ambient finish I´m assuming you left them 
> to the
> default value. Which is 0.1 and therefore emitting light! So if you want 
> to get
> rid of ambient finish you have to write ambient 0 for every single 
> material.
> (My favorite is diffuse 0.9, ambient 0, looks realistic in most cases, 
> except
> for some metals maybe.)
> If ambient is left to the default you lose the "shadows inside the shadow" 
> if
> you know what I mean.

Yes indeed, that is why I always #default{ambient 0 diffuse 1} at the start 
of my scenes. However, examining my code again, I discovered that in this 
scene I stupidly set this default *only* when no radiosity is used!!! 
Arrrgh!!! That might account for part of the problem. I could indeed also 
the default diffuse a bit. I have made several scenes even with a diffuse of 
0.5, but I must say that was a bit overdone maybe.

> Using a single light source like you did, is the best (only) approach in 
> your
> case, using
> radiosity instead to take care of the shadow areas and should look great 
> in
> your image. What I´m trying to say is that you scene has a -great- 
> potential
> light wise.
>
> It also seems that you are basing your radiosity settings on the default 
> Pov
> values which I have found fast but useless in most cases, the colors 
> usually are
> way to bright and saturated and everything looks flat and artificial.

Hmm. Yes, I see what you mean. There are several settings that I am not 
really sure of and I mostly leave them alone. Those I always experiment with 
in each scene are error_bound, count, recursion_limit, gray_threshold. To 
tell the truth, I always feel a bit unconfortable with radiosity. I 
certainly lack a deep knowledge of the thing, unfortunately.

> I have a little tutorial on my site, if you haven´t seen it. Maybe the 
> radiosity
> settings there can be used as a base for you settings, even thought the
> situation is somewhat different. They are originally
> based on the Pov manual as the "best" but always have to be tweaked. Maybe 
> you
> should check it out.
>
> http://www.simnet.is/hildurka/content/tut1page.htm

Shame on me! Of course I know your tutorial! And as it goes, I forgot about 
it in the moment I could use it most. I shall always remain amazed by the 
strange workings of the mind  :-)
Thanks Hildur, for putting me on track again. Lessons are learned the hard 
way, especially by lazy pupils....

> Also I don´t know what system your are using and if you have the patience 
> to
> wait on a slow render. But it´s usually worth the few extra hours (or 
> days! ;)

I don't mind having render times of several days (my latest for the new 
TC-RTC round is already in that stage), and I agree that it is worth the 
while. I am going to experiment further with this, especially as I am not 
really happy with the scene in its present state, which is the reason I am 
surprised at even getting a second place at all...

Thanks for your comments Hildur. I do appreciate them very much.

Thomas


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From: Hildur K 
Subject: Re: TC-RTC comments
Date: 2 Sep 2008 10:35:01
Message: <web.48bd1625f7aedb2eb34d91590@news.povray.org>
"Thomas de Groot" <t.d### [at] internlDOTnet> wrote:
> "Hildur K." <hil### [at] 3dcafemailevery1net> schreef in bericht
> news:web.48bc094ff7aedb2e80197cfe0@news.povray.org...


> Hmm. Yes, I see what you mean. There are several settings that I am not
> really sure of and I mostly leave them alone. Those I always experiment with
> in each scene are error_bound, count, recursion_limit, gray_threshold. To
> tell the truth, I always feel a bit unconfortable with radiosity. I
> certainly lack a deep knowledge of the thing, unfortunately.

To be honest, I have no real idea about how radiosity works either. I´m not a
mathematical/scientific person. Stubborn maybe. I simply took the "ideal"
settings from the manual and worked from there. I think I made something like a
million test renderings to "get the feel" of what works, looking at the work of
other people to see what is really possible. A very time consuming hobby.

 Lessons are learned the hard
> way, especially by lazy pupils....

Sounds like the perfect description of me... how did you know ;)

> I don't mind having render times of several days (my latest for the new
> TC-RTC round is already in that stage), and I agree that it is worth the
> while. I am going to experiment further with this, especially as I am not
> really happy with the scene in its present state, which is the reason I am
> surprised at even getting a second place at all...

There are some very good elements in your scene. The characters are simply
great. They look very much alive. Composition and modeling is great... The
overall situation is working very well.

If you write to me directly (contact through my site) I can email you a small
zip file I already have, containing some basic radiosity code I made for an
outdoor solution. I think I also made a description to go with it.

Could save you some time, heck, that´s why I made it. The trial and error method
is good and valid but should we all be inventing the wheel?

Hildur


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From: Thomas de Groot
Subject: Re: TC-RTC comments
Date: 2 Sep 2008 11:27:05
Message: <48bd2309$1@news.povray.org>
"Hildur K." <hil### [at] 3dcafemailevery1net> schreef in bericht 
news:web.48bd1625f7aedb2eb34d91590@news.povray.org...
>
> Lessons are learned the hard
>> way, especially by lazy pupils....
>
> Sounds like the perfect description of me... how did you know ;)

LOL! Two of a kind then  :-)

> There are some very good elements in your scene. The characters are simply
> great. They look very much alive. Composition and modeling is great... The
> overall situation is working very well.

Yes, it was mainly the radiosity issue I was unhappy with. I did a rapid 
test and indeed: the scene is already much better. I really wonder how I 
came to keep the ambient switched on... blackout probably.

> If you write to me directly (contact through my site) I can email you a 
> small
> zip file I already have, containing some basic radiosity code I made for 
> an
> outdoor solution. I think I also made a description to go with it.

Sounds excellent! I shall do that!

> Could save you some time, heck, that´s why I made it. The trial and error 
> method
> is good and valid but should we all be inventing the wheel?

I agree. I always learn a lot from the work of others in the first place. 
Then, experimenting further, is important to get the feel of the thing. This 
is something which I have not yet done enough with radiosity.

Thomas


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